Mr. Hammes joined Kirkland & Ellis in 1985 and has been a partner since 1991. Mr. Hammes became Chairman of Kirkland's 15-person Global Management Executive Committee in 2010 and served three terms in the role. Mr. Hammes was a founding partner of the San Francisco office opened in 2003 and the Palo Alto office opened in 2008. Mr. Hammes also led the Kirkland’s expansion into Asia with the opening of offices in Hong Kong, Shanghai and Beijing, starting in 2007. He also led and oversaw the significant transformation and growth of the Firm’s offices in New York and London.

Mr. Hammes has concentrated his practice on structuring and negotiating complex business transactions including mergers, acquisitions, leveraged buyouts, going private transactions, and private equity compensation and governance matters. Described by clients in Chambers Global as a "lawyer who grasps the big picture with every transaction", Mr. Hammes was named to Chambers Global, The World's Leading Lawyers for Business every year since 2001 and to The Best Lawyers in America every year since 2006. He was named to Crain's "Who's Who" in Chicago Business feature each year since 2012.

Mr. Hammes serves on the University of Wisconsin Foundation Board of Directors the Northwestern School of Law Dean's Advisory Board and the Board of Trustees of the Ravinia Festival Association.