Exhibit 99.1

ALTERRA CAPITAL REPORTS FIRST QUARTER 2012 RESULTS

Net Operating Income of $0.66 per Diluted Share

Diluted Book Value per Share Growth including Dividends of 3.3%

HAMILTON, BERMUDA, May 9, 2012—Alterra Capital Holdings Limited (NASDAQ: ALTE; BSX: ALTE.BH) (“Alterra”) today reported net income of $79.0 million, or $0.77 per diluted share, for the first quarter of 2012, compared to a net loss of $46.7 million, or $0.44 per diluted share, for the same quarter of 2011.

Net operating income for the first quarter of 2012 was $67.8 million, or $0.66 per diluted share, compared to a net operating loss of $24.7 million, or $0.23 per diluted share, for the same quarter of 2011. Annualized net operating return on average shareholders’ equity for the first quarter of 2012 was 9.6%.

W. Marston (Marty) Becker, President and Chief Executive Officer of Alterra, said: “We started the year off with a solid quarter and the financial results reflect a good balance between underwriting and investment performance. Our operating return on equity was just under 10%, making this the fourth consecutive quarter in which we have grown book value per share. Alterra’s newer segments and teams in U.S. insurance, Alterra at Lloyd’s and Latin America are still maturing, and with modest levels of earned premium are showing expense ratios that are higher than our ultimate expectations. While our selected loss ratios for these segments and teams will remain conservative until we see more actual loss experience, we are pleased with their progress to date.”

“The market has firmed materially for any risk that has property catastrophe exposure, and has firmed somewhat for certain other lines of business. It is encouraging to us that the remaining rates are no longer going down, and that terms and conditions are generally more balanced. We continue to expect positive rate movement through the balance of 2012, and believe Alterra is well positioned to take advantage of underwriting opportunities as better times return,” Mr. Becker concluded.

First quarter 2012 results for Alterra include:

Gross premiums written (“GPW”) and net premiums written (“NPW”) from property and casualty underwriting for the first quarter of 2012 were as shown in the following table, with the increase/decrease compared to the same quarter of 2011:

Balance Sheet

Total invested assets, including cash and cash equivalents, were $7,804.5 million as of March 31, 2012, a decrease of $10.2 million from December 31, 2011. As of March 31, 2012, 95.9% of the fixed maturities portfolio (by carrying value) was investment-grade, an increase from 94.4% as of December 31, 2011. As of March 31, 2012, the weighted average book yield of Alterra’s cash and fixed maturities portfolio was 3.36%, and the weighted average duration was 4.2 years.

Under a Board-approved share repurchase authorization, Alterra repurchased 2,065,877 common shares during the first quarter of 2012 at an average price of $23.56 per share for a total of $48.7 million. As of March 31, 2012, $205.7 million remained under the Board-approved share repurchase authorization.

Shareholders’ equity was $2,851.3 million as of March 31, 2012, an increase of 1.5% from December 31, 2011. Diluted book value per share as of March 31, 2012 was $27.67. Including dividends declared, diluted book value per share growth for the first quarter of 2012 was 3.3%, and was 11.3% for the twelve months ended March 31, 2012. Not included in shareholders’ equity as of March 31, 2012 were $144.3 million of unrecognized gains on held-to-maturity securities, which represented $1.40 in unrecognized diluted book value per share.

A copy of Alterra’s first quarter financial supplement is available on Alterra’s website at www.alterracap.com.

Alterra will host a conference call on Thursday, May 10, 2012 at 10:00 am (EDT) to discuss these results and related matters. The conference call can be accessed via telephone by dialing 1-888-679-8040 (toll-free U.S.) or 1-617-213-4851 (international) and using access code 41021175. A live broadcast of the conference call will also be available through Alterra’s website at www.alterracap.com.

Alterra Capital Holdings Limited is a global enterprise dedicated to providing diversified specialty insurance and reinsurance products to corporations, public entities and property and casualty insurers.

Non-GAAP Financial Measures

In presenting Alterra’s results, management has included and discussed net operating income, net operating income per diluted share, annualized net operating return on average shareholders’ equity and diluted tangible book value per share. These measures are “non-GAAP financial measures” as defined in Regulation G. Management believes that these non-GAAP financial measures, which may be defined differently by other companies, allow for a more complete understanding of Alterra’s business. These

measures, however, should not be viewed as a substitute for measures determined in accordance with U.S. GAAP. The reconciliation of these measures to their respective most directly comparable U.S. GAAP financial measures is presented in the attached financial information in accordance with Regulation G.

Cautionary Note Regarding Forward-Looking Statements

This release includes forward-looking statements that reflect Alterra’s current views with respect to future events and financial performance. In particular, statements regarding future rate movements are forward looking statements. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those suggested by such statements. For further information regarding cautionary statements and factors affecting Alterra’s future results, please refer to the most recent reports on Form 10-K and Form 10-Q and other documents filed by Alterra with the SEC. Alterra undertakes no obligation to update or revise publicly any forward-looking statement whether as a result of new information, future developments or otherwise.

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED BALANCE SHEETS

(Expressed in thousands of United States Dollars, except per share and share amounts)

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (Unaudited)

(Expressed in thousands of United States Dollars, except per share and share amounts)

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS’ EQUITY (Unaudited)

(Expressed in thousands of United States Dollars)

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)

(Expressed in thousands of United States Dollars)

SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:

Interest paid totaled $11,137 and $11,120 for the three months ended March 31, 2012 and 2011, respectively.

Income taxes paid totaled $4,197 and $79 for the three months ended March 31, 2012 and 2011, respectively.

ALTERRA CAPITAL HOLDINGS LIMITED

SCHEDULE OF SUPPLEMENTAL SEGMENT DATA–THREE MONTHS ENDED MARCH 31, 2012 (Unaudited)

(Expressed in thousands of United States Dollars)

SCHEDULE OF SUPPLEMENTAL SEGMENT DATA–THREE MONTHS ENDED MARCH 31, 2011 (Unaudited)

(Expressed in thousands of United States Dollars)