Early returns showed de Blasio trouncing his Republican opponent, Joe Lhota. The city board of elections reported de Blasio had more than 70 percent of the vote, while Lhota's name was on a total of four ballot lines but had just over 20 percent.
The last Democrat to win was David Dinkins, the city's first black mayor. Four years later, Republican Rudolph Giuliani unseated Dinkins and, after two terms, was followed by Mayor Michael Bloomberg, who ran once as a Republican and twice as an independent.
De Blasio ran an aggressively liberal campaign, talking about income inequality and the need for affordable housing. Voters appear to have responded.
Darrian Smith, a school custodian in Brooklyn, told The New York Times he was upset about the aggressive policing pushed by Giuliani and Bloomberg, especially what has become known as "stop and frisk."
"When I look at Mr. de Blasio, I see a bright light at the end of the tunnel," he said.
Lhota, a former Wall Street banker who served as a deputy mayor under Giuliani, was believed to be a formidable candidate when he entered the race, the Times said. In the end, however, he failed to match de Blasio in his own campaign and in fundraising.
On Election Day, de Blasio mobilized 10,000 volunteers to 500 for his opponent.