At a news conference in City Hall, Mr. de Blasio presented the decision as the final resolution of what had been one of the most fraught political and cultural sagas of his mayoralty. The firing of Officer Pantaleo “ended a chapter that has brought our people so much pain and so much fear these last five years,” he said.

“Today we have finally seen justice done,” said Mr. de Blasio, who is running for president on his credentials as a progressive Democrat. “We must devote ourselves to this simple goal: No one should have to go through the agony that the city has gone through here. Let this be the last tragedy.”

Mr. de Blasio blamed the Justice Department for taking five years before deciding not to pursue civil rights charges, saying “the place that was synonymous with making things right failed us.” The mayor also sought to calm police officers angered by Officer Pantaleo’s firing, urging New Yorkers to thank them for their efforts.

At a new conference a few blocks away, Mr. Lynch said rank-and-file officers were outraged and “brokenhearted.” He called on Governor Andrew M. Cuomo to remove Mr. de Blasio and Commissioner O’Neill from office for reckless leadership. “There’s no confidence for the leadership at City Hall and One Police Plaza,” he said. “The leadership has abandoned ship and left our police officers on the streets, alone.”

Officer Pantaleo’s lawyer, Stuart London, said his client plans to sue in state Supreme Court to be reinstated. “He is disappointed, upset, but has a lot of strength,” Mr. London said. “He wants to go forward.”

Outside Police Headquarters, Mr. Garner’s mother, Gwen Carr, joined supporters in the afternoon — some holding signs that read “FIRED” over Officer Pantaleo’s photograph — to demand that the mayor and the police commissioner also fire the 11 other police officers who took part in her son’s arrest. Only one — Sgt. Kizzy Adonis, who was the first supervisor to arrive on the scene — faces disciplinary charges.

“They all need to lose their jobs,” she said.

“Pantaleo, you may have lost your job, but I lost a son,” she added. “You cannot replace that. You can get another job, maybe at Burger King.”