“Let’s see if he can do what he’s promised for us,” said Baltazar Sanchez, 30, one of hundreds of Salvadorans dancing, waving flags and blowing whistles in a plaza that Bukele had revitalized when he was mayor.
“After 30 years of two parties, we’ve been dealt the best hand.”
Gang violence has made tiny El Salvador one of the world’s most murderous countries in the past few years, driving Salvadorans to flee to the north.
Among his campaign promises, Mr Bukele, an avid social media user who often sports a black leather jacket, said he would push infrastructure projects to limit such migration.
Since the end of its civil war in 1992, El Salvador has been governed by the ruling leftist Farabundo Marti National Liberation Front (FMLN) and its rival, conservative Nationalist Republican Alliance (ARENA).
Though he describes himself as from the left and was expelled from the FMLN, Mr Bukele has formed a coalition including a right-wing party that together has just 11 seats in the legislature.
Outside the hotel in San Salvador where Bukele waited for the results, a group of supporters set off fireworks, beat drums and danced as early figures came in.
“Yes, we did it! Yes, we did it!” they chanted.