Jeremy Clay, a partner in the firm’s London office, was appointed the new managing partner of Chicago-based Mayer Brown LLP, according an announcement issued this week.Kenneth S. Geller, Clay’s predecessor, is stepping down from the post he held since 2009. Clay joined Mayer Brown when the firm merged with London-based Rowe & Maw in 2002. In June 2012, Clay was appointed to the firm’s management committee, where he will continue to serve in his new role as managing partner.“When Ken decided to …