Exhibit 10.1

AMENDMENT NO. 6
TO
CREDIT AGREEMENT

AMENDMENT NO. 6 (“Amendment No. 6”), dated as of December 1, 2010, to the Credit
Agreement, dated as of December 21, 2006, by and between Alterra Bermuda Limited
(f/k/a Alterra Insurance Limited), a Bermuda company (the “Borrower”) and The
Bank of Nova Scotia (the “Lender”), as amended by Amendment No. 1, dated as of
December 20, 2007, Amendment No. 2, dated as of December 18, 2008, Amendment
No. 3, dated as of December 17, 2009, Amendment No. 4, dated as of May 3, 2010,
Amendment No. 5, dated as of August 30, 2010 (as the same may be amended,
supplemented or otherwise modified from time to time, the “Credit Agreement”).

RECITALS

I. Capitalized terms used herein and not herein defined shall have the meanings
set forth in the Credit Agreement.

II. The Borrower desires to amend the Credit Agreement upon the terms and
conditions herein contained, and the Lender has agreed thereto.

Accordingly, in consideration of the Recitals and the covenants, conditions and
agreements hereinafter set forth, and for other good and valuable consideration,
the receipt and adequacy of which are hereby acknowledged, the parties hereto
agree as follows:

1. The defined term “HP U.S. Subsidiary” contained in Section 1.1 of the Credit
Agreement is hereby amended and restated in its entirety as follows:

“HP U.S. Subsidiary” means each of (i) Alterra Holdings USA Inc., a Delaware
corporation (f/k/a Harbor Point U.S. Holdings, Inc.), (ii) Alterra Reinsurance
USA Inc., a Connecticut corporation (f/k/a Harbor Point Reinsurance U.S., Inc.),
(iii) Alterra Reinsurance Services Inc., a Delaware corporation (f/k/a Harbor
Point Services, Inc.), and (iv) Alterra Finance LLC, a Delaware limited
liability company.

2. Section 6.3 of the Credit Agreement is hereby amended by deleting the phrase
“may sell, transfer, convey or lease all or any substantial part of its assets”
that appears in the proviso at the end thereof and replacing it with the phrase
“may be sold, transferred, conveyed or leased”.

3. Paragraphs 1 and 2 hereof shall not be effective until the following
condition is satisfied (the date, if any, on which such condition shall have
first been satisfied being referred to herein as the “Amendment No. 6 Effective
Date”):

(a) The Lender shall have received from the Borrower either (i) a counterpart of
this Amendment No. 6 executed on behalf of the Borrower or (ii) written evidence
satisfactory to the Lender (which may include telecopy transmission of a signed
signature page of this Amendment No. 6) that the Borrower has executed a
counterpart of this Amendment No. 6;

4. Notwithstanding anything to the contrary contained herein, this Amendment
shall cease to be effective and shall be null and void if the following
conditions are not satisfied within ten days of the Amendment No. 6 Effective
Date:

(a) The Lender shall have received a closing certificate, duly executed by the
proper parties and substantially in the form of Exhibit A hereto;

(b) All fees and expenses payable to the Lender and invoiced to the Borrower
(including the reasonable fees and expenses of counsel to the Lender) shall have
been paid.

5. The Borrower (i) reaffirms and admits the validity and enforceability against
the Borrower of each Credit Document and all of its obligations thereunder,
(ii) agrees and admits that it has no defense to or offset against any such
obligation, and (iii) represents and warrants that, as of the date of the
execution and delivery hereof by the Borrower, no Default has occurred and is
continuing.

6. This Amendment No. 6 may be executed in any number of counterparts, each of
which shall be original and all of which shall constitute one agreement. It
shall not be necessary in making proof of this Amendment No. 6 to produce or
account for more than one counterpart signed by the party to be charged.

7. This Amendment No. 6 shall be governed by, and construed in accordance with,
the laws of the State of New York, without regard to conflict of laws principles
that would require the application of the laws of another jurisdiction.

8. Except as amended hereby, the Credit Agreement shall in all other respects
remain in full force and effect.

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 6 to the
Credit Agreement to be duly executed and delivered by their proper and duly
authorized officers as of the day and year first above written.

ALTERRA BERMUDA LIMITED

By:
Name:
Title:

THE BANK OF NOVA SCOTIA

By:
Name:
Title: