Mr. de Blasio, 52, was formally sworn in shortly after midnight in a brief ceremony in front of his family's rowhouse in Park Slope, Brooklyn.

A Democrat, he begins his term as an emblem of resurgent liberalism, offering hope to progressive activists and officeholders across the country -- but also as an untested chief executive whose management of the city will be closely scrutinized.

Previously the city's public advocate and before that a city councilman, Mr. de Blasio rose out of obscurity in a crowded Democratic primary field as he shaped his campaign around the "tale of two cities" -- a succinct summation of the rising income inequality he vowed he would urgently address as the next mayor.

He won a landslide victory on Nov. 5 over the Republican candidate, Joseph J. Lhota, seizing on an anxiety among voters that the city was increasingly becoming a gilded enclave for the rich, and vowing a sharp turn from the administration of his predecessor, Michael R. Bloomberg.

Mr. de Blasio will appear at City Hall on Wednesday with his wife, Chirlane McCray; his 19-year-old daughter, Chiara; and his 16-year-old son, Dante.

He will be ceremonially sworn in by former President Clinton, in whose administration he served as a regional official in the Department of Housing and Urban Development. Mr. de Blasio will be sworn in using a Bible once owned by Franklin Delano Roosevelt.

Mr. de Blasio's inauguration last week team made 1,000 tickets available to the public, which were claimed within two hours.

Dozens of other New Yorkers have been invited to join Mr. de Blasio on stage at the event, including an engineer from Queens who emigrated from Bangladesh; a Staten Island couple whose home was damaged by Hurricane Sandy; and a fast-food worker from Brooklyn.

Mr. de Blasio's successor as public advocate, Letitia James, who had been a city councilwoman, will also be inaugurated on Wednesday, as will the new city comptroller, Scott M. Stringer, who had been the Manhattan borough president.