Thompson was declared the winner with 74.8 percent of the vote, while Hynes received 25.2 percent, with 99 percent of precincts reporting, capping one of the campaign season's most contentious contests.
It was the second time this election season that Hynes lost to Thompson. The outgoing DA was previously beaten during the Democratic primary, before running in the general election on the Republican line.
"I am truly grateful and deeply humbled, for the people of Brooklyn have taken a man who started out in life with the odds stacked against him and made him the next district attorney of Brooklyn," Thompson said in his acceptance speech.
Hynes' loss came after his two-decade tenure as Brooklyn's top prosecutor was marred by several recent scandals.
Hynes has been accused of not prosecuting sexual abuse cases in the insular Hasidic community, and his office also faced criticism after an investigation revealed problems with former Brooklyn detective Louis Scarcella's tactics, causing a judge to overturn a murder conviction earlier this year. One of the investigated cases, which was prosecuted by Hynes, resulted in parole for the convicted man just last week.
"We must ensure that no man or woman is convicted wrongfully again," Thompson said in hs speech. "We must free all the people who have been convicted wrongfully."
Thompson dealt with questions of his own early on, especially over his handling of his client Nafissatou Diallo’s accusation of rape against Dominique Strauss-Kahn, the French former head of the International Monetary Fund. The criminal charges against Strauss-Kahn were ultimately dropped, though a settlement was reached in the civil suit.
Thompson first faced Hynes in the Democratic primary in September, pulling off a surprise win over the incumbent DA.
Normally, Thompson's primary victory would have all but ensured him a general election win in heavily Democratic Brooklyn. But Hynes decided to cross party lines in October and to try for a rematch against Thompson as a Republican and Conservative Party candidate.
The general election grew ugly, as Thompson's supporters charged Hynes with race baiting, and Hynes' supporters accused Thompson of accepting help from former Brooklyn Democratic Party boss and convicted felon Clarence Norman.