In the first quarter, we participated in nearly 40 public market transactions that raised more than $22 billion in total proceeds.
Global and US announced M&A dollar volume increased 95% and 164% respectively compared to the first quarter of 2020 and increased 3% and 13% respectively from a strong fourth quarter.
First quarter adjusted net revenues of $669.9 million grew 54% year-over-year.
First quarter advisory fees of $512.1 million was 43% year-over-year.
Based on current consensus, estimates and actual results, we expect to maintain our number-four ranking on advisory fees among all publicly traded investment banking firms for the last 12 months and to grow our market share relative to these same firms.
Our first quarter underwriting fees of $79.3 million more than tripled year-over-year.
First quarter commissions and related revenue of $53.5 million decreased 4% year-over-year as volumes declined relative to the elevated levels in the first quarter of 2020.
First quarter asset management and administration fees of $17.8 million increased 16% year-over-year on higher AUM, which was $10.6 billion at quarter end, an increase of 11% year-over-year.
Turning to expenses, our adjusted compensation revenue for the first quarter is 59%.
First quarter non-comp costs of $72.7 million declined 12% year-over-year.
Our non-compensation ratio for the first quarter is 10.9%.
First quarter adjusted operating income and adjusted net income of $201.8 million and $162.5 million increased 145% and 181% respectively.
We delivered a first quarter adjusted operating margin of 30.1% and a first quarter adjusted earnings per share of $3.29 increased 172% year-over-year.
We returned $275.3 million to shareholders during the quarter through dividends and the repurchase of 1.9 million shares.
Our Board declared a dividend of $0.68, an increase of 11.5%.
Our Board also approved a refresh of our share repurchase authority to $750 million.
On top of our strong financial performance, we sustained our number-one league table ranking in the dollar volume of announced M&A transactions both globally and in the US among independent firms for the last 12 months ending March 31 and in the first quarter of 2021.
We served as the lead advisor on Grab's $40 billion IPO buyer, a SPAC merger, the largest tech merger this year, the largest SPAC merger in history and the largest pipe issued in conjunction with a SPAC merger at a little over $4 billion.
And we also served as the sole advisor to Nuance on its pending $19.7 billion sale to Microsoft, the second largest tech merger this year.
When we first acquired ISI almost seven years ago, we identified one of the most important opportunities created by that transaction to be our ability to increase our underwriting revenues to perhaps $75 million to a $100 million of revenue per year over the ensuing few years.
In fact, three of the past four quarters, including the first quarter of 2021, where in just one quarter, within that $75 million to a $100 million target that we had set for the full year.
Our investments in ECM have earned us a place in the top 20 for underwriting revenue as estimated by Dealogic when bot deals are excluded.
The breaking into the Top 10 currently seems challenging given our aversion to block trades and our independent balance sheet light approach.
First, we are intensely focused on continuing to position our business for sustaining long-term growth by number one, providing outstanding advice and execution of our clients as we continue to advise them on their most important strategic financial and capital decisions; number two, by continuing to enhance our coverage of the most significant client groups, including our initiatives around the Evercore 100 and financial sponsors; number three, investing to further deepen and broaden our capabilities by continuing to build out certain industry groups, geographies and product capabilities.
For the first quarter of 2021, net revenues, net income and earnings per share on a GAAP basis were $662 million, $144 million and $3.25 respectively.
Our GAAP tax rate for the first quarter was 16.1% compared to 25.8% for the prior year period.
On a GAAP basis, our share count was 44.5 million shares for the first quarter.
The share count for adjusted earnings per share was $49.4 million for the quarter.
Firmwide non-compensation costs per employee were approximately $40,000 for the first quarter, down 9% on a year-over-year basis.
On March 29th, we issued $38 million of aggregate principal amount of unsecured senior notes with a 1.97% coupon through a private placement.
And finally, at the end of the quarter, we held $411 million in cash and cash equivalents and $873 million in investment securities down from year-end due to compensation-related payments and strong return of capital.

Summary:
First quarter adjusted net revenues of $669.9 million grew 54% year-over-year.
We delivered a first quarter adjusted operating margin of 30.1% and a first quarter adjusted earnings per share of $3.29 increased 172% year-over-year.
Our Board declared a dividend of $0.68, an increase of 11.5%.
For the first quarter of 2021, net revenues, net income and earnings per share on a GAAP basis were $662 million, $144 million and $3.25 respectively.