George Russell finished a fortunate second for Mercedes, to slash Antonelli's advantage to 25 points after nine rounds, with fellow Briton Lewis Hamilton completing the podium for Ferrari but under investigation for a potential yellow flag breach.
"Finally!" Leclerc said over the radio after claiming his first victory for nearly two years.
"This one felt particularly good, even if I wished it was a more normal ending."
Australia's Oscar Piastri missed out on points in 11th place, the McLaren driver's challenge effectively ended early on after being made to make a pit stop for sustaining damage at the end of Lap 1.
Piastri's team-mate Lando Norris was fourth behind Hamilton. The result leaves the Aussie driver sixth in the drivers' championship with his McLaren team third in the constructors table, but still without a Grand Prix win this season.
"We have a hell of a lot to improve," said Norris afterwards.
The race safety car at Silverstone was triggered by Red Bull's Max Verstappen crashing out with four laps remaining and it stayed out to the end despite a message suggesting it would pit to allow one last lap of racing.
Antonelli, who started on pole position, had been second and closing in on Leclerc with 11 laps to go when he slowed and alerted the team to a problem with the car.
He was ninth across the line after ignoring the team's pleas to retire the car so he could fight for the final points places.
He ended up outside the points anyway. The Italian dropped to 16th with a time penalty for going off-track as he wrangled his damaged car around the corners.
Second place for Russell revives his title chances even though the British driver had struggled for competitive pace all weekend. Antonelli's lead shrinks from 43 points over Russell to 25, the value of a single race win.
Russell had been fourth in the sprint, fourth in qualifying and was battling Verstappen for fourth in the race before the late drama.
It was "a very unlucky race... then very lucky," Russell said.
