Lewis Hamilton's slim title hopes took a further blow as he crashed his McLaren early on. Hamilton slipped to fifth in the standings, 113 points behind Vettel, who has a 92-point advantage over second-placed Webber.
Ferrari's Fernando Alonso is third ahead of Jenson Button, despite the Briton overtaking the Spaniard late in the race to claim third place at Spa. Button, who won the last race in Hungary, was left to rue what might have been had he not started the race way down in 13th spot on the grid.
Vettel secured pole position for the ninth time in 12 races this season. But he had not won any of the last three GPs in Britain, Germany and Hungary, and only one of the last five heading into Spa, prompting speculation that he was losing his grip on the title.
Vettel's jubilation was evident at ending that winless run as he stood on top of his Red Bull after the race, and pumped his fists in delight.
The Belgian Jérôme D'Ambrosio (Virgin-Cosworth) came in 17th.