John Finley, co-chair of Simpson Thacher & Bartlett’s mergers and acquisitions group, is moving to take the top in-house spot at Blackstone Group, according to a statement the private equity fund released Wednesday.

Finley has worked on many landmark transactions in the last couple of years, including his representation of Lehman Brothers in the sale of its North American operations to Barclays and Mars Inc.’s move to purchase the Wm. Wrigley Jr. Co. for $23.1 billion in a leveraged buyout-style deal.