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Simpson Thacher Adds Boston Dealmaker

08.12.25

Simpson Thacher & Bartlett LLP today announced that William N. Lay has joined the Firm’s Boston office as a Partner in the Mergers and Acquisitions Practice.

“Will has sharp commercial judgment and a strong track record advising on complex deals, and we are excited to welcome him to Simpson Thacher,” said Eric Swedenburg, Head of Simpson Thacher’s Mergers and Acquisitions Practice. “His addition reflects the continued momentum of growth in our Boston office and our broader strategy to continue expanding Simpson Thacher’s transactional capabilities in key markets to meet clients’ demands in an increasingly dynamic deal environment.”

Will has extensive experience advising private equity sponsors and public companies on complex M&A, carve-outs, joint ventures and other strategic transactions. His work spans numerous industries, including healthcare and life sciences, technology, retail and manufacturing. He joins Simpson Thacher from another international law firm.

“Will is a great addition to the dynamic and growing team we are building in Boston,” said Josh Bonnie, Co-Managing Partner of the Boston office.

“Simpson Thacher’s reputation for excellence in M&A is second to none,” said Will. “I’m excited to join a team that is not only shaping the market but that is also deeply committed to clients, collaboration and growth in Boston.”

Since launching in 2024, Simpson Thacher’s Boston office has grown rapidly to meet client demand across transactional, regulatory and litigation matters. Repeatedly recognized around the world by Chambers, Legal 500, The American Lawyer, Law360 and many others, Simpson Thacher’s Mergers and Acquisitions Practice is an industry leader unrivaled in its reputation and unique in its breadth. The team has advised on many of the most prominent U.S. and international transactions of the past several decades as well as on deals with an aggregate value of more than $1.5 trillion from 2020—2024 alone (Bloomberg). The Firm’s clients include public and private companies, founder-owned and family-owned businesses, investors and boards. The scale and depth of Simpson Thacher’s private equity experience also gives the Firm insight into the needs of participants across the sector, making it the firm of choice for many of the world’s most sophisticated private equity firms.

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