Chicago Mayor Rahm Emanuel will not seek a third term in office, he announced Tuesday morning, a stunning reversal that will leave the city's politics in turmoil.

Emanuel, 58, first won election in 2011, succeeding the legendary Richard M. Daley. His two terms in office had been marred by repeated waves of violence, especially in low-income minority neighborhoods, and frequent clashes with education activists, labor allies and the city's African American community.

"Today, the time has come to make another tough choice. As much as I love this job, and will always love this city and its residents, I've decided not to seek re-election," Emanuel said at a City Hall press conference. "This has been the job of a lifetime, but it is not a job for a lifetime."

Emanuel had insisted through this year he would seek a third term in 2019, bolstered by a campaign account stocked with more than $10 million and aided by a field of little-known challengers who had struggled to define themselves.

But Emanuel's political standing had degraded over time. He increased property taxes to new highs, in response to a growing pension crisis. Critics blasted his handling of a police shooting that left an unarmed black teenager dead. And he angered many with a plan that shuttered 50 public schools.

Violence continues to plague the city. Last month, 64 people were shot in the course of a single weekend.

"Rahm is practiced in the art of politics, and he can see the difficulty for incumbents, for the energy on the side of the more progressive candidates," said Thomas Bowen, a Democratic strategist who worked for Emanuel during his first campaign for mayor. "His re-election was going to be extremely difficult. He is not somebody who goes into extremely difficult battles that he doesn't think he has an advantage. And he doesn't right now."

Twelve candidates have already filed papers to run for mayor. They include Paul Vallas, the former head Chicago Public Schools, and former police superintendent Garry McCarthy, both of whom are strident Emanuel critics. Former Police Board president Lori Lightfoot, once a federal prosecutor, and a handful of activists, businessmen and tech entrepreneurs are also in the race.

More candidates may join the race before the November 26 filing deadline.

Bowen said there is no clear front-runner in the race as of yet. Chicago voters head to the polls on February 26 to winnow the field; if no candidate gets a majority of the vote, the first- and second-place finishers will face off in an April 2 runoff.

Emanuel once appeared on a long steady climb to national prominence. After serving in senior positions in two Democratic administrations, including as President Obama's chief of staff, and in Democratic leadership in Congress, some expected him to mount a presidential campaign at some point.

That is unlikely now. Standing beside his wife Amy Rule on Tuesday, Emanuel said they intended to chart a new path, now that his three children are in college.