Clarke was first elected to city council in 1999 and has spent 12 years serving as council president.
Clarke says he will not be a candidate in the 2023 election but will serve out the remainder of his term.
"I love my job, serving the residents of the 5th Council District," he said in a statement. "It's the best job in the world. And I enjoy the trust of serving my colleagues as President of this body."
"I'm confident in our members and their abilities," his statement continued. "It's been the privilege of a lifetime to serve the people of Philadelphia. And I'm excited and looking forward to continuing to serve the public in meaningful ways."
He started his City Hall career as a staffer to then-council member John Street, and replaced Street in council when Street ran for mayor in 1999.
Clarke represents the 5th District, which is based in North Philadelphia.
His departure means Philadelphia will have a new council president, mayor, and city controller next January.