Announcing the result on Sunday, Ahmat Mahamat Bachir, the president of Chad's Independent National Election Commission, said Deby won the May 3 election with 77.5% of the vote, handing him a third five-year term as president of the central African oil producer.
Despite a rebel attack on the capital, N'Djamena, three weeks before the polls, Deby's re-election was widely considered a formality after opposition parties boycotted the election, calling it a farce.
Western diplomats had reported a low, unenthusiastic participation at the polls which appeared to hand Deby only a shaky mandate, but Bachir said turnout was 61%.
Rebels who launched the April 13 attack on N'Djamena, in which hundreds of people were killed, have already rejected Deby's offer of dialogue.
Deby, 54, a French-trained pilot, has ruled Chad since his Patriotic Salvation Movement (MPS) rebel group seized power in a revolt.