<PAGE>


                                                                   Exhibit 10.12

                                VOTING AGREEMENT

                  This VOTING AGREEMENT, dated as of December 21, 2002 (this
"Agreement"), is entered into by and among Black Bear Fund II, L.L.C., a limited
liability company duly organized under the laws of the State of California
("Black Bear"), and each of the other shareholders and noteholders of XM
Satellite Radio Holdings Inc., a corporation organized under the laws of the
State of Delaware (the "Company"), identified on the signature pages hereto
(each of Black Bear and such other shareholders and noteholders of the Company,
a "Shareholder" and, collectively, the "Shareholders").

                  WHEREAS, the Shareholders own of record and/or beneficially
the shares of Class A common stock, par value $.01 per share, of the Company
("Class A Common Stock"), and/or 8.25% Series C Convertible Redeemable Preferred
Stock, par value $.01 per share ("Series C Preferred Stock" and, together with
the Class A Common Stock, the "Capital Stock"), set forth opposite their
respective names on Schedule A hereto, and desire to enter into this Agreement
with respect to such shares of Capital Stock;

                  WHEREAS, the Company and its subsidiary, XM Satellite Radio
Inc., a Delaware corporation ("XM"), propose to: (i) offer to exchange a
combination of (a) 14% Senior Secured Discount Notes due 2009 of XM, (b)
warrants to purchase shares of Class A Common Stock (the "Exchange Warrants"),
and (c) cash, for some or all of the outstanding 14% Senior Secured Notes due
2010 of XM; (ii) issue 10% Senior Secured Discount Convertible Notes due 2009
(the "New Notes") to a group comprised of qualified institutional buyers and
accredited investors, including some of the Shareholders or their affiliates
(the "New Noteholders"); (iii) issue and sell, on or before the closing of the
transactions described in this recital, to the extent determined to be desirable
by the Company, shares of Class A Common Stock, with or without warrants to
purchase shares of Class A Common Stock, or after the closing to the extent
contemplated by the letter agreement between the Company and the BayStar Group,
in accordance with Section 4(2) of the Securities Act of 1933, as amended, or
pursuant to a registration statement under the Securities Act, including the
proposed sale of 5,555,556 shares of Class A Common Stock to U.S. Trust Company
and the issuance of a warrant to purchase 900,000 shares of Class A Common
Stock, (iv) issue to General Motors Corporation or an affiliate thereof ("GM")
Series GM 10% Senior Secured Convertible Notes due 2009 (the "GM Notes") in lieu
of making certain guaranteed payments owed to GM from 2003 to 2006, and in
connection therewith to (x) amend XM's distribution agreement with GM (the
"Distribution Agreement") to provide for the issuance of the GM Notes and for
the payment, at the Company's option, of up to $35,000,000 of certain subscriber
bounty payments required thereunder through the issuance of Class A Common
Stock, (y) enter into a $100,000,000 senior secured credit facility with GM to
fund certain revenue share payments owed to GM under the Distribution Agreement
and other amounts which may be owed to GM, and (z) issue a warrant to GM to
purchase 10,000,000 shares of Class A Common Stock (the "GM Warrant"); (v) enter
into a Second Amended and Restated Shareholders and Noteholders Agreement (the
"Shareholders and Noteholders Agreement"), pursuant to which the New Noteholders
and GM will be granted certain consent and other rights; (vi) enter into a
Second Amended and Restated Registration Rights Agreement, and (vii) execute,
deliver and perform such other documents, and take all other actions, necessary
or desirable to carry out the foregoing (collectively, the "Concurrent Financing
Transactions"); and

                  WHEREAS, in order to facilitate the Concurrent Financing
Transactions, the Shareholders have agreed to enter into this Agreement and, in
the case of Shareholders other than Black Bear, execute and deliver the Proxy
contemplated hereby.

<PAGE>

                  NOW, THEREFORE, the parties hereto, in consideration of the
foregoing, the mutual covenants and agreements contained herein and for other
good and valuable consideration, the receipt and sufficiency of which hereby are
acknowledged, and intending to be legally bound hereby, agree as follows:

         SECTION 1.     AGREEMENT TO VOTE IN FAVOR OF PROPOSED CHARTER AMENDMENT

                  (a)   Each Shareholder acknowledges and understands that the
Company will be required to obtain stockholder approval of an amendment to the
Company's restated certificate of incorporation to increase the number of
authorized shares of Class A Common Stock to 600,000,000 to permit the Company
to validly reserve for issuance a sufficient number of shares of Class A Common
Stock as may be required to effectuate the issuances or potential issuances of
Class A Common Stock or otherwise in connection with the Concurrent Financing
Transactions and for general corporate purposes (such number, the "Required
Number"). Such approval will require (i) the affirmative vote of persons holding
a majority of the shares of Class A Common Stock outstanding on the record date
set in advance of the meeting called to consider the proposed amendment, voting
as a separate class, (ii) the affirmative vote of persons holding 60% or more of
the shares of Series C Preferred Stock outstanding on the record date set in
advance of the meeting called to consider the proposed amendment, and (iii) the
affirmative vote of persons holding a majority of the shares of Class A Common
Stock and Series C Preferred Stock outstanding on the record date set in advance
of the meeting called to consider the proposed amendment, voting together as a
single class.

                  (b)   Each Shareholder hereby agrees, effective immediately
following the closing of the Concurrent Financing Transactions (the "Effective
Time"), to appear, or cause the holder of record (the "Record Holder") of any
such Capital Stock beneficially owned by it on any applicable record date (a
"Record Date") to appear, in person or by proxy, for the purpose of obtaining a
quorum at any annual or special meeting of shareholders of the Company, and at
any adjournment of either of them (a "Meeting"), called for the purpose of
considering the approval of an amendment to the Company's restated certificate
of incorporation to increase the number of authorized shares of Class A Common
Stock from 225,000,000 to 600,000,000 (the "Proposed Charter Amendment").

                  (c)   Each Shareholder further agrees that at any such Meeting
such Shareholder shall vote, or cause the Record Holder to vote, in person or by
proxy (including, in the case of all Shareholders except Black Bear, through the
Proxy to be granted in accordance with Section 2 hereof) all of the shares of
Capital Stock, and any other voting interests of the Company directly or
indirectly owned beneficially or of record by such Shareholder on the Record
Date set for such meeting, in favor of the Proposed Charter Amendment.

                  (d)   To the extent inconsistent with the foregoing provisions
of this Section 1, each Shareholder revokes any and all previous proxies with
respect to shares of Capital Stock owned or hereafter acquired beneficially
and/or of record by such Shareholder and agrees not to grant any proxy or enter
into any voting trust or other agreement or arrangement with respect to the
voting of any Capital Stock or any rights, options, warrants or other rights to
acquire Capital Stock, except as provided herein. Notwithstanding the foregoing,
it is understood and acknowledged that nothing in this Agreement shall be
construed to restrict any Shareholder from transferring any Capital Stock.

         SECTION 2.     PROXY; FURTHER ASSURANCES

                                      - 2 -

<PAGE>

                  (a)   Contemporaneously with the execution of this Agreement,
each Shareholder (other than Black Bear) has delivered to Black Bear a proxy in
the form attached to this Agreement as Exhibit A, which shall be irrevocable to
the fullest extent permitted by law, with respect to the shares referred to
therein (a "Proxy"). The Shareholders agree and acknowledge that Black Bear
shall not be entitled to vote any shares of Capital Stock covered by any such
Proxy at any Meeting until after the Effective Time.

                  (b)   Each Shareholder shall agree to supplement such Proxy to
the extent needed to include shares of Capital Stock hereafter acquired, and
shall perform such further acts and execute such further documents and
instruments as may reasonably be required to vest in Black Bear the power to
carry out and give effect to the provisions of this Agreement. Without limiting
the generality of the foregoing, none of the parties hereto shall enter into any
agreement or arrangement (or alter, amend or terminate any existing agreement or
arrangement) or transaction if such action would materially impair or materially
interfere with the ability of any party to effectuate, carry out and comply with
all of the terms of this Agreement.

         SECTION 3.     REPRESENTATIONS AND WARRANTIES OF EACH SHAREHOLDER

                  Each Shareholder hereby, severally and not jointly, represents
and warrants as follows:

                  (a)   Such Shareholder has the legal capacity and all other
power and authority necessary to enter into this Agreement, to perform the
obligations hereunder and to consummate the transactions contemplated hereby.
This Agreement and, if applicable, the Proxy have been duly executed and
delivered by such Shareholder and constitute the legal, valid and binding
obligations of such Shareholder, enforceable against such Shareholder in
accordance with their respective terms, except as such enforceability may be
limited by bankruptcy, insolvency, reorganization, moratorium and other similar
laws of general applicability relating to or affecting creditor's rights
generally and by the application of general principles of equity.

                  (b)   The execution and delivery of this Agreement and, if
applicable, the Proxy by such Shareholder do not, and the performance of this
Agreement and, if applicable, the Proxy by such Shareholder will not, (i)
conflict with or violate any law, regulation, court order, judgment or decree
applicable to such Shareholder or by which it or any of its properties is or may
be bound or affected, or (ii) result in or constitute (with or without notice or
lapse of time) any breach of or default under, or give to any other person (with
or without notice or lapse of time), any right of termination, amendment,
acceleration or cancellation, or result (with or without notice or lapse of
time) in the creation of any encumbrance, pledge or mortgage, or the formation
of any contract, option or other agreement or understanding with respect to any
encumbrance, pledge or mortgage (any of the foregoing, an "Encumbrance") or
restriction on any Capital Stock of such Shareholder pursuant to, any contract
or agreement to which such Shareholder is a party or by which such Shareholder
or any of its affiliates or properties is or may be bound or affected.

                  (c)   The execution and delivery of this Agreement and, if
applicable, the Proxy do not, and the performance of this Agreement and, if
applicable, the Proxy will not require any consent or approval or other action
by any person.

                  (d)   The shares of Capital Stock reflected on Schedule A as
being owned by such Shareholder are the only shares of Capital Stock of the
Company owned beneficially or of record by such

                                      - 3 -

<PAGE>

Shareholder (other than shares the beneficial ownership of which has been
disclaimed by such Shareholder pursuant to filings made pursuant to the
Securities Exchange Act of 1934, as amended). Such Shareholder has the sole
power to vote and transfer such Shareholder's shares of Capital Stock. The
shares and certificates representing such shares held by such Shareholder are
now owned as indicated on Schedule A by such Shareholder, free and clear of all
liens, claims or any other Encumbrances, except for any such Encumbrances or the
Proxy arising under this Agreement or the Amended and Restated Shareholders
Agreement, dated August 8, 2000, by and among the Company and the other parties
thereto, and except for Encumbrances which would not affect their power to vote
such Shareholder's shares of Capital Stock as provided in this Agreement.

         SECTION 4.     SPECIFIC PERFORMANCE

                  The parties agree that irreparable damage would occur in the
event that any provision of this Agreement or the Proxy was, or is, not
performed in accordance with its specific terms or was, or is, otherwise
breached. Each Shareholder agrees that, in the event of any breach or threatened
breach by such Shareholder of any covenant or obligation contained in this
Agreement or in the Proxy, Black Bear shall be entitled (in addition to any
other remedy that may be available to it, including monetary damages) to (a) a
decree or order of specific performance to enforce the observance and
performance of such covenant or obligation, and (b) an injunction restraining
such breach or threatened breach. Each Shareholder further agrees that neither
Black Bear nor any other person shall be required to obtain, furnish or post any
bond or similar instrument in connection with or as a condition to obtaining any
remedy referred to in this Section 4, and each Shareholder irrevocably waives
any objection to the imposition of such relief or any right he may have to
require the obtaining, furnishing or posting of any such bond or similar
instrument. Black Bear hereby undertakes to use commercially reasonable efforts
to enforce the observance and performance by each of the other Shareholders of
the covenants and obligations contained in this Agreement.

         SECTION 5.     SURVIVAL

                  All representations, warranties and agreements made by the
Shareholders in this Agreement shall survive until the Expiration Date.

         SECTION 6.     ASSIGNMENT; BINDING EFFECT

                  Except as provided herein, neither this Agreement nor any of
the interests or obligations hereunder may be assigned or delegated by any
Shareholder without the prior written consent of the non-assigning party, which
consent shall not be unreasonably withheld, and any attempted or purported
assignment or delegation of any of such interests or obligations shall be void.
No consent of Black Bear or any other Shareholder shall be required as a
condition to the sale, assignment, disposition or other transfer, including by
means of an Encumbrance, of any shares of Capital Stock by any Shareholder, it
being expressly agreed to and acknowledged that the provisions of this Agreement
will not be binding upon, inure to the benefit of, any such transferee. Subject
to the preceding two sentences, this Agreement shall be binding upon, and inure
to the benefit of, the Shareholders. Nothing in this Agreement is intended to
confer on any person (other than Black Bear) any rights or remedies of any
nature.

                                      - 4 -

<PAGE>

         SECTION 7.     AMENDMENT AND WAIVER

                  This Agreement shall not be amended, altered or modified
except by an instrument in writing duly executed and delivered on behalf of each
of the parties hereto. No failure on the part of any Shareholder to exercise any
power, right, privilege or remedy under this Agreement, and no delay on the part
of any Shareholder in exercising any power, right, privilege or remedy under
this Agreement, shall operate as a waiver of such power, right, privilege or
remedy; and no single or partial exercise of any such power, right, privilege or
remedy shall preclude any other or further exercise thereof or of any other
power, right, privilege or remedy. No Shareholder shall be deemed to have waived
any claim available to it arising out of this Agreement, or any power, right,
privilege or remedy of such Shareholder under this Agreement, unless the waiver
of such claim, power, right, privilege or remedy is expressly set forth in a
written instrument duly executed and delivered on behalf of such Shareholder;
and any such waiver shall not be applicable or have any effect except in the
specific instance in which it is given.

         SECTION 8.     SEVERABILITY

                  If any provision of this Agreement or any part of any such
provision is held under any circumstances to be invalid or unenforceable in any
jurisdiction, then (a) such provision or part thereof shall, with respect to
such circumstances and in such jurisdiction, be deemed amended to conform to
applicable laws so as to be valid and enforceable to the fullest possible
extent, (b) the invalidity or unenforceability of such provision or part thereof
under such circumstances and in such jurisdiction shall not affect the validity
or enforceability of such provision or part thereof under any other
circumstances or in any other jurisdiction, and (c) the invalidity or
unenforceability of such provision or part thereof shall not affect the validity
or enforceability of the remainder of such provision or the validity or
enforceability of any other provision of this Agreement. Each provision of this
Agreement is separable from every other provision of this Agreement, and each
part of each provision of this Agreement is separable from every other part of
such provision.

         SECTION 9.     NOTICES

                  All notices and other communications given or made pursuant
hereto shall be in writing and shall be deemed to have been duly given or made
as of the date delivered, mailed or transmitted, and shall be effective upon
receipt, if delivered personally, mailed by registered or certified mail
(postage prepaid, return receipt requested) to the parties at the following
addresses (or at such other address for a party as shall be specified by like
changes of address) or sent by facsimile to the fax number specified below:

                  If to a Shareholder other than Black Bear:

                           To such Shareholder's address
                           or fax number as set forth
                           on Schedule A attached hereto

                  If to Black Bear:

                           c/o Eastbourne Capital Management, L.L.C.
                           1101 Fifth Avenue, Suite 160
                           San Rafael, California 94901

                                      - 5 -

<PAGE>

                           Attention:       Eric M. Sippel,
                                            Chief Operating Officer
                           Fax No.:  (415) 448-1246

         SECTION 10.    ENTIRE AGREEMENT

                  This Agreement, the Proxy and any other documents delivered by
the parties in connection herewith constitute the entire agreement between the
parties with respect to the subject matter hereof and thereof and supercede all
prior agreements and understandings between the parties with respect thereto.

         SECTION 11.    COUNTERPARTS

                  This Agreement may be executed and delivered in one or more
counterparts, and by the different parties hereto in separate counterparts, each
of which when executed and delivered shall be deemed to be an original but all
of which taken together shall constitute one and the same agreement.

         SECTION 12.    TERMINATION

                  This Agreement and all of the parties' rights and obligations
hereunder shall terminate on the first to occur of (a) the date on which the
Concurrent Financing Transactions are validly terminated pursuant to the terms
of the definitive documents evidencing them, or (b) the date on which the last
Meeting held to consider the Proposed Charter Amendment has been convened and
adjourned, or (c) March 31, 2003 (such earliest date, the "Expiration Date").

         SECTION 13.    GOVERNING LAW

                  This Agreement shall be governed by, and construed in
accordance with, the laws of the State of Delaware, regardless of the laws that
might otherwise govern under applicable principles of conflicts of law.

         SECTION 14.    NON-EXCLUSIVITY.

                  The rights and remedies of any Shareholder under this
Agreement are not exclusive of or limited by any other rights or remedies which
it may have, whether at law, in equity, by contract or otherwise, all of which
shall be cumulative (and not alternative). Without limiting the generality of
the foregoing, the rights and remedies of the Shareholders under this Agreement,
and the obligations and liabilities of the Shareholders under this Agreement,
are in addition to their respective rights, remedies, obligations and
liabilities under common law requirements and under all applicable statutes,
rules and regulations. Nothing in this Agreement shall limit any of any
Shareholder's obligations under any agreement between any Shareholders; and
nothing in any such agreement shall limit any of any Shareholder's obligations,
rights and remedies under this Agreement.

                            [SIGNATURE PAGES FOLLOW]

                                      - 6 -

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have duly executed and delivered
this Agreement, or have caused this Agreement to be executed and delivered on
their behalf, as of the date first above written.


                                     SHAREHOLDERS:

<PAGE>

                                     BLACK BEAR FUND I, L.P.
                                     By: Eastbourne Capital Management, L.L.C.,
                                     its general partner


                                     By:  /s/ Eric M. Sippel
                                         ---------------------------------------
                                     Name: Eric M. Sippel
                                     Title: Chief Operating Officer

                                     BLACK BEAR FUND II, L.L.C.
                                     By: Eastbourne Capital Management, L.L.C.,
                                     its manager


                                     By:  /s/ Eric M. Sippel
                                         ---------------------------------------
                                     Name: Eric M. Sippel
                                     Title: Chief Operating Officer

                                     BLACK BEAR OFFSHORE MASTER FUND LIMITED
                                     By: Eastbourne Capital Management, L.L.C.,
                                     its investment adviser and attorney in fact


                                     By:  /s/ Eric M. Sippel
                                         ---------------------------------------
                                     Name: Eric M. Sippel
                                     Title: Chief Operating Officer

                      [Signature Page to Voting Agreement]

<PAGE>

                                 CLEAR CHANNEL INVESTMENTS, INC.


                                 By: /s/ Randall T. Mays
                                     -------------------------------------------
                                 Name: Randall T. Mays
                                      ------------------------------------------
                                 Title: Executive Vice President
                                        ----------------------------------------


                                 HUGHES ELECTRONICS CORPORATION


                                 By:   /s/ Patrick T. Doyle
                                     -------------------------------------------
                                 Name: Patrick T. Doyle
                                      ------------------------------------------
                                 Title: Vice President, Treasurer and Controller
                                       -----------------------------------------


                                 TELCOM--XM INVESTORS, L.L.C.


                                 By:   /s/ Rajendra Singh
                                    --------------------------------------------
                                 Name: Rajendra Singh
                                      ------------------------------------------
                                 Title: President
                                       -----------------------------------------


                                 GEORGE HAYWOOD

                                   /s/ George Haywood
                                 -----------------------------------------------

                      [Signature Page to Voting Agreement]

<PAGE>

                                   SCHEDULE A

<TABLE>
<CAPTION>
                                                  NUMBER OF SERIES C           NUMBER OF SHARES OF CLASS A
INVESTOR NAME AND ADDRESS FOR NOTICES                  SHARES                         COMMON STOCK
<S>                                                     <C>                             <C>
Black Bear Fund I, L.P.                                    0                            3,173,433
c/o Eastbourne Capital Management, L.L.C.
1101 Fifth Avenue, Suite 160
San Rafael, California 94901
Attention: Eric M. Sippel,
           Chief Operating Officer
Fax No.: (415) 448-1246

Black Bear Fund II, L.L.C.                                 0                             362,100
c/o Eastbourne Capital Management, L.L.C.
1101 Fifth Avenue, Suite 160
San Rafael, California 94901
Attention: Eric M. Sippel,
           Chief Operating Officer
Fax No.: (415) 448-1246

Black Bear Offshore Master Fund Limited                    0                            6,491,765
c/o Eastbourne Capital Management, L.L.C.
1101 Fifth Avenue, Suite 160
San Rafael, California 94901
Attention: Eric M. Sippel,
           Chief Operating Officer
Fax No.: (415) 448-1246

Clear Channel Investments, Inc.                            0                            8,329,877
200 E. Basse Road
San Antonio, TX 78209
Attention: Ken Wyker, Esq.
Fax No.: (210) 822-2299

Hughes Electronics Corporation                          20,000                          7,268,184
200 N. Sepulveda Boulevard
El Segundo, CA 90245

Telcom--XM Investors, L.L.C.                                0                           2,411,211
211 North Union Street, Suite 300
Alexandria, VA 22314

George Haywood                                              0                           5,623,281
C/o Cronin & Vris, LLP
380 Madison Avenue
24th Floor
New York, NY 10017
</TABLE>

<PAGE>

                                    EXHIBIT A

                            Form of Irrevocable Proxy

                  The undersigned Shareholder of XM Satellite Radio Holdings
Inc., a Delaware corporation (the "Company"), hereby irrevocably (to the fullest
extent permitted by law) appoints and constitutes Black Bear II, L.L.C., a
limited liability company organized under the laws of the State of California
("Black Bear"), the attorney and proxy of the undersigned, with full power of
substitution and resubstitution, to the full extent of the undersigned's voting
rights with respect to (a) the outstanding shares of Class A Common Stock,
Series C Preferred Stock, or any other voting capital stock of the Company
(collectively, the "Capital Stock") owned of record by the undersigned as of the
date of this proxy, which shares are specified on the final page of this proxy,
and (b) any and all other shares of Capital Stock of the Company which the
undersigned may acquire on or after the date hereof. Upon the execution hereof,
all prior proxies given by the undersigned with respect to any of the Capital
Stock are hereby revoked, and the undersigned agrees that no subsequent proxy
will be given with respect to any of the Capital Stock.

                  This proxy is (i) irrevocable, (ii) coupled with an interest,
and (iii) granted in connection with the execution and delivery of the Voting
Agreement dated as of the date hereof among Black Bear, the undersigned and
certain other Shareholders of the Company (the "Voting Agreement"). Capitalized
terms used but not defined in this proxy shall have the respective meanings
ascribed to such terms in the Voting Agreement.

                  The proxy named above (and its successors) will, following the
Effective Time but prior to the Expiration Date, be empowered, and is hereby
authorized and directed to vote the Capital Stock at any meeting of the
shareholders of the Company, however called, in favor of the approval of the
Proposed Charter Amendment. The undersigned may vote the Capital Stock on all
other matters.

                  This proxy shall be binding upon the representatives,
successors and assigns of the undersigned (including any transferee of any of
the Capital Stock).

                  If any provision of this proxy or any part of any such
provision is held under any circumstances to be invalid or unenforceable in any
jurisdiction, then (a) such provision or part thereof shall, with respect to
such circumstances and in such jurisdiction, be deemed amended to conform to
applicable laws so as to be valid and enforceable to the fullest possible
extent, (b) the invalidity or unenforceability of such provision or part thereof
under such circumstances and in such jurisdiction shall not affect the validity
or enforceability of such provision or part thereof under any other
circumstances or in any other jurisdiction, and (c) the invalidity or
unenforceability of such provision or part thereof shall not affect the validity
or enforceability of the remainder of such provision or the validity or
enforceability of any other provision of this proxy. Each provision of this
proxy is separable from every other provision of this proxy, and each part of
each provision of this proxy is separable from every other part of such
provision.

                  This proxy shall terminate upon the Expiration Date.

<PAGE>

Date: _______________, 200__


                                         ---------------------------------------
                                         Shareholder's Name

                                         Number of shares of Class A Common
                                         Stock of the Company owned of record as
                                         of the date of this proxy:


                                         ---------------------------------------

                                         Number of shares of Series C Preferred
                                         Stock of the Company owned of record as
                                         of the date of this proxy:


                                         ---------------------------------------

                                       ii