<PAGE>

    As filed with the Securities and Exchange Commission on July 30, 1999.

                                                           Registration No. 333-

================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549

                                   FORM S-8

                         REGISTRATION STATEMENT UNDER
                          THE SECURITIES ACT OF 1933

                            ACT Manufacturing, Inc.
            (Exact name of registrant as specified in its charter)


<TABLE>
<CAPTION>
                     Massachusetts                                                 04-2777507
<S>                                                                   <C>
(State or other jurisdiction of incorporation or organization)        (I.R.S. Employer Identification No.)
</TABLE>

                                 2 Cabot Road
                          Hudson, Massachusetts 01749
                                (978) 567-4000
              (Address of Principal Executive Offices) (Zip Code)

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


         Amended and Restated 1990 Equity Incentive Plan (assumed from
                             CMC Industries, Inc.)
                     Amended and Restated 1995 Stock Plan

                           (Full title of the plans)

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

                                 John A. Pino
                     President and Chief Executive Officer
                            ACT Manufacturing, Inc.
                                 2 Cabot Road
                          Hudson, Massachusetts 01749
                                (978) 567-4000
          (Name and address including zip code and telephone number,
                  including area code, of agent for service)

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

                                   Copy to:
                             John A. Meltaus, Esq.
                        TESTA, HURWITZ & THIBEAULT, LLP
                                125 High Street
                          Boston, Massachusetts 02110
                                (617) 248-7000

     Approximate date of commencement of proposed sale to the public: As soon as
practicable after this Registration Statement becomes effective.

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

================================================================================
<PAGE>

                        CALCULATION OF REGISTRATION FEE

================================================================================
<TABLE>
<CAPTION>
                                                         Proposed                Proposed
                                                          Maximum                Maximum
         Title of                   Amount               Offering               Aggregate             Amount of
       Securities to                 to be               Price Per               Offering            Registration
       be Registered              Registered               Share                  Price                  Fee
--------------------------------------------------------------------------------------------------------------------
<S>                               <C>                    <C>                    <C>                  <C>
Amended and Restated 1990
Equity Incentive Plan
Common Stock                         771,758            $11.8358/(1)/            $ 9,134,373.3364           $2,539.36
(Par Value $.01)                     160,685            $15.4690/(2)/            $ 2,485,636.2650           $  691.01


Amended and Restated 1995
Stock Plan
Common Stock                       1,000,000            $15.4690/(2)/            $15,469,000                $4,300.39
(Par Value $.01)

TOTAL:                             1,932,443                                                                $7,530.76
                                   shares
</TABLE>
================================================================================

(1)  All such shares are issuable upon exercise of outstanding options with
     fixed exercise prices. Pursuant to Regulation C, Rule 457(h)(1) under the
     Securities Act of 1933, as amended, the aggregate offering price and the
     fee have been computed upon the basis of the price at which the options may
     be exercised. The offering price per share set forth for such shares is the
     weighted average exercise price per share at which such options are
     exercisable.

(2)  The price of $15.469 per share, which is the average of the high and low
     prices of the common stock of the registrant reported on the Nasdaq
     National Market on July 29, 1999, is set forth solely for purposes of
     calculating the filing fee pursuant to Rule 457(c) and (h) and has been
     used only for those shares which have not yet been granted.

<PAGE>

                                      -3-

                                    PART I

             INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS


Item 1.   Plan Information.
          ----------------

         The documents containing the information specified in this Item 1 will
be sent or given to employees, directors or others as specified by Rule
428(b)(1). In accordance with the rules and regulations of the Securities and
Exchange Commission (the "Commission") and the instructions to Form S-8, such
documents are not being filed with the Commission either as part of this
Registration Statement or as prospectuses or prospectus supplements pursuant to
Rule 424.

Item 2.   Registrant Information and Employee Plan Annual Information.
          -----------------------------------------------------------

         The documents containing the information specified in this Item 2 will
be sent or given to employees as specified by Rule 428(b)(1). In accordance with
the rules and regulations of the Commission and the instructions to Form S-8,
such documents are not being filed with the Commission either as part of this
Registration Statement or as prospectuses or prospectus supplements pursuant to
Rule 424.

                                    PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT


Item 3.   Incorporation of Documents by Reference.
          ---------------------------------------

         The following documents filed with the Commission are incorporated by
reference in this Registration Statement:

         (a)   Registrant's Annual Report on Form 10-K for the fiscal year ended
               December 31, 1998.

         (b)   Registrant's Quarterly Report on Form 10-Q for the period ended
               March 31, 1999.

         (c)   All other reports filed pursuant to Section 13(a) or 15(d) of the
               Securities Exchange Act of 1934, as amended (the "Exchange Act"),
               since the end of the fiscal year ended December 31, 1998.

         (d)   The section entitled "Description of Registrant's Securities to
               be Registered," contained in the Registrant's Registration
               Statement on Form 8-A, filed on February 15, 1995 pursuant to
               Section 12(g) of the Exchange Act.

         All documents subsequently filed with the Commission by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to
the filing of a post-effective amendment which indicates that all securities
offered herein have been sold or which
<PAGE>

                                      -4-

deregisters all securities then remaining unsold, shall be deemed to be
incorporated by reference in this Registration Statement and to be a part hereof
from the date of filing of such documents.

Item 4.   Description of Securities.
          -------------------------

         Not applicable.

Item 5.   Interest of Named Experts and Counsel.
          -------------------------------------

         Not applicable.

Item 6.   Indemnification of Directors and Officers.
          -----------------------------------------

         Section 67 of Chapter 156B of the Massachusetts General Laws provides
that a corporation may indemnify its directors and officers to the extent
specified in or authorized by (i) the articles of organization, (ii) a by-law
adopted by the stockholders, or (iii) a vote adopted by the holders of a
majority of the shares of stock entitled to vote on the election of directors.
In all instances, the extent to which a corporation provides indemnification to
its directors and officers under Section 67 is optional. In its Amended and
Restated By-Laws, the Registrant has elected to commit to provide
indemnification to its directors and officers in specified circumstances.
Generally, Article V, Section 2 of the Registrant's Amended and Restated By-Laws
indemnifies directors and officers of the Registrant against liabilities and
expenses arising out of legal proceedings brought against them by reason of
their status as directors or officers or by reason of their agreeing to serve,
at the request of the Registrant, as a director or officer with another
organization. Under this provision, a director or officer of the Registrant
shall be indemnified by the Registrant for all costs and expenses (including
attorneys' fees), judgments, liabilities and amounts paid in settlement of such
proceedings, even if he is not successful on the merits, if he acted in good
faith in the reasonable belief that his action was in the best interests of the
Registrant. The Registrant's Board of Directors may authorize advancing
litigation expenses to a director or officer at his request upon receipt of an
undertaking by any such director or officer to repay such expenses if it is
ultimately determined that he is not entitled to indemnification for such
expenses.

         Article 6 of the Registrant's Second Restated Articles of Organization,
as amended, eliminates the personal liability of the Registrant's directors to
the Registrant or its stockholders for monetary damages for breach of a
director's fiduciary duty, except to the extent Chapter 156B of the
Massachusetts General Laws prohibits the elimination or limitation of such
liability.

         The Registrant maintains directors' and officers' liability insurance
for the benefit of its directors and certain of its officers.
<PAGE>

                                      -5-

Item 7.   Exemption From Registration Claimed.
          -----------------------------------

         Not applicable.

Item 8.   Exhibits.
          --------

         Exhibit No.                Description of Exhibit
         ----------                 ----------------------

         Exhibit 4.1                Second Restated Articles of Organization of
                                    the Registrant (filed as Exhibit 3.1 to the
                                    Registrant's Annual Report on Form 10-K for
                                    the year ended December 31, 1995, and
                                    incorporated herein by reference).

         Exhibit 4.2                Articles of Amendment to the Second Restated
                                    Articles of Organization of the Registrant.

         Exhibit 4.3                Amended and Restated By-Laws of the
                                    Registrant, as amended (filed as Exhibit 3.2
                                    to the Registrant's Registration Statement
                                    on Form S-1, File No. 33-89532, and
                                    incorporated herein by reference).

         Exhibit 4.4                Specimen certificate representing the Common
                                    Stock of the Registrant (filed as Exhibit
                                    4.1 to the Registrant's Registration
                                    Statement on Form S-1, File No. 33-89532,
                                    and incorporated herein by reference).

         Exhibit 4.5                Amended and Restated 1995 Stock Plan.

         Exhibit 4.6                Amended and Restated 1990 Equity Incentive
                                    Plan (assumed from CMC Industries, Inc.).

         Exhibit 5.1                Opinion of Testa, Hurwitz & Thibeault, LLP.

         Exhibit 23.1               Consent of Testa, Hurwitz & Thibeault, LLP
                                    (contained in Exhibit 5.1).

         Exhibit 23.2               Consent of Deloitte & Touche LLP.

         Exhibit 24.1               Power of Attorney (included as part of the
                                    signature page to this Registration
                                    Statement).

Item 9.   Undertakings.
          ------------

         (a)   The undersigned Registrant hereby undertakes:

               (1)  To file, during any period in which offers or sales are
                    being made, a post-effective amendment to this Registration
                    Statement:
<PAGE>

                                      -6-

                           (i)      To include any prospectus required by
                                    Section 10(a)(3) of the Securities Act of
                                    1933;


                           (ii)     To reflect in the prospectus any facts or
                                    events arising after the effective date of
                                    the Registration Statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the
                                    information set forth in the Registration
                                    Statement;

                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the Registration
                                    Statement or any material change to such
                                    information in the Registration Statement;

                                    provided, however, that paragraphs (a)(1)(i)
                                    --------  -------
                                    and (a)(1)(ii) do not apply if the
                                    information required to be included in a
                                    post-effective amendment by those paragraphs
                                    is contained in periodic reports filed with
                                    or furnished to the Commission by the
                                    Registrant pursuant to Section 13 or Section
                                    15(d) of the Securities Exchange Act of 1934
                                    that are incorporated by reference in the
                                    Registration Statement.

                  (2)      That, for the purpose of determining any liability
                           under the Securities Act of 1933, each such
                           post-effective amendment shall be deemed to be a new
                           Registration Statement relating to the securities
                           offered therein, and the offering of such securities
                           at that time shall be deemed to be the initial bona
                           fide offering thereof.

                  (3)      To remove from registration by means of a
                           post-effective amendment any of the securities being
                           registered which remain unsold at the termination of
                           the offering.

          (b)     The undersigned Registrant hereby undertakes that, for
                  purposes of determining any liability under the Securities Act
                  of 1933, each filing of the Registrant's annual report
                  pursuant to Section 13(a) or Section 15(d) of the Securities
                  Exchange Act of 1934 (and, where applicable, each filing of an
                  employee benefit plan's annual report pursuant to Section
                  15(d) of the Securities Exchange Act of 1934) that is
                  incorporated by reference in the Registration Statement shall
                  be deemed to be a new registration statement relating to the
                  securities offered therein, and the offering of such
                  securities at that time shall be deemed to be the initial bona
                  fide offering thereof.

         (c)      Insofar as indemnification for liabilities arising under the
                  Securities Act of 1933 may be permitted to directors, officers
                  and controlling persons of the Registrant pursuant to the
                  foregoing provisions, or otherwise, the Registrant has been
                  advised that in the opinion of the Securities and Exchange
                  Commission such indemnification is against public policy as
                  expressed in the Securities Act of 1933 and is, therefore,
                  unenforceable. In the event that a claim for indemnification
                  against such liabilities (other than the payment by the
<PAGE>

                                      -7-

                  Registrant of expenses incurred or paid by a director, officer
                  or controlling person of the Registrant in the successful
                  defense of any action, suit or proceeding) is asserted by such
                  director, officer or controlling person in connection with the
                  securities being registered, the Registrant will, unless in
                  the opinion of its counsel the matter has been settled by
                  controlling precedent, submit to a court of appropriate
                  jurisdiction the question whether such indemnification by it
                  is against public policy as expressed in the Act and will be
                  governed by the final adjudication of such issue.


                 [Remainder of Page Intentionally Left Blank]
<PAGE>

                                      -8-

                                  SIGNATURES


         Pursuant to the requirements of the Securities Act of 1933, the
Registrant, ACT Manufacturing, Inc., certifies that it has reasonable grounds to
believe that it meets all of the requirements for filing on Form S-8 and has
duly caused this Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the Town of Hudson, Commonwealth of
Massachusetts, on this 30th day of July, 1999.

                             ACT MANUFACTURING, INC.


                             By:  /s/ John A. Pino
                                ------------------------
                                  John A. Pino
                                  President and Chief Executive Officer


                               POWER OF ATTORNEY

         We, the undersigned officers and directors of ACT Manufacturing, Inc.,
hereby severally constitute and appoint John A. Pino and Jeffrey B. Lavin, and
each of them singly, our true and lawful attorneys, with full power to them and
each of them singly, to sign for us in our names in the capacities indicated
below, any amendments to this Registration Statement on Form S-8 (including
post-effective amendments), and to file the same, with all exhibits thereto and
other documents in connection therewith, with the Securities and Exchange
Commission, and generally to do all things in our names and on our behalf in our
capacities as officers and directors to enable ACT Manufacturing, Inc. to comply
with the provisions of the Securities Act of 1933, as amended, hereby ratifying
and confirming our signatures as they may be signed by our said attorneys, or
any of them, to said Registration Statement and all amendments thereto.

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.

            Signature                    Title(s)                   Date
            ---------                    --------                   ----

         /s/ John A. Pino      Chairman of the Board, President   July 30, 1999
         ----------------
         John A. Pino          and Chief Executive Officer
                               (Principal Executive Officer)
<PAGE>

                                      -9-

<TABLE>
         <S>                      <C>                                  <C>
         /s/ Jeffrey B. Lavin     Vice President of  Finance, Chief    July 30, 1999
         ----------------------
         Jeffrey B. Lavin         Financial Officer, Treasurer
                                  and Clerk (Principal Financial
                                  and Accounting Officer)


         /s/ Bruce R. Gardner     Director                             July 30, 1999
         ---------------------
         Bruce R. Gardner


         /s/ Donald G. Polich     Director                             July 30, 1999
         -----------------------
         Donald G. Polich


         /s/ Edward T. Cuddy      Director                             July 30, 1999
         --------------------
         Edward T. Cuddy


         /s/ David S. Lee         Director                             July 30, 1999
         -----------------
         David S. Lee


         /s/ Frederick W. Gibbs   Director                             July 30, 1999
         ----------------------
         Frederick W. Gibbs
</TABLE>
<PAGE>

                                 Exhibit Index
                                 -------------

Item 8. Exhibits.
        --------

<TABLE>
<CAPTION>
        Exhibit No.    Description of Exhibit
        ----------     ----------------------
        <S>            <C>
        Exhibit 4.1    Second Restated Articles of Organization of the
                       Registrant (filed as Exhibit 3.1 to the
                       Registrant's Annual Report on Form 10-K for the
                       year ended December 31, 1995, and incorporated
                       herein by reference).

        Exhibit 4.2+   Articles of Amendment to the Second Restated
                       Articles of Organization of the Registrant.

        Exhibit 4.3    Amended and Restated By-Laws of the Registrant,
                       as amended (filed as Exhibit 3.2 to the
                       Registrant's Registration Statement on Form S-1,
                       File No. 33-89532, and incorporated herein by
                       reference).

        Exhibit 4.4    Specimen certificate representing the Common
                       Stock of the Registrant (filed as Exhibit 4.1 to
                       the Registrant's Registration Statement on Form S-1,
                       File No. 33-89532, and incorporated herein by
                       reference).

        Exhibit 4.5+   Amended and Restated 1995 Stock Plan.

        Exhibit 4.6+   Amended and Restated 1990 Equity Incentive Plan
                       (assumed from CMC Industries, Inc.).

        Exhibit 5.1+   Opinion of Testa, Hurwitz & Thibeault, LLP.

        Exhibit 23.1   Consent of Testa, Hurwitz & Thibeault, LLP
                       (contained in Exhibit 5.1).

        Exhibit 23.2+  Consent of Deloitte & Touche LLP.

        Exhibit 24.1   Power of Attorney (included as part of the
                       signature page to this Registration Statement).
</TABLE>
----------------
+ Filed herewith