Chicago Mayor-elect Lori Lightfoot (D) announced Mark Flessner, a Holland & Knight partner since 2012, will serve as the city’s next corporation counsel and lead the city’s 450-person law department.

Flessner was named to the post late May 16. He will succeed Edward Siskel, a former Washington-based WilmerHale partner.

Lightfoot, elected April 2, will be inaugurated as Chicago’s 56th mayor May 20.

An experienced trial attorney, Flessner also served as a federal prosecutor in Chicago for more than a decade. His current practice includes advising clients in civil, criminal, and regulatory matters. He’s represented clients in the health care, retail, manufacturing, insurance, and financial sectors.

The department he will lead employs more than 250 lawyers and is responsible for providing legal counsel and representation for the mayor and the city’s more than 40 departments. The law department is involved in litigation, transactional, and legislative matters, and it’s also responsible for enforcing the city’s Municipal Code.

Lightfoot, like Flessner, worked for a Big Law firm and is a former federal prosecutor. She worked at Mayer Brown before her election to the position of mayor.

Flessner will succeed Edward Siskel, who has served as corporate counsel since February 2017. Siskel is also a former deputy White House Counsel under President Barack Obama who earlier in his career clerked for Supreme Court Associate Justice John Paul Stevens.