Ferrari's Fernando Alonso, now his closest rival, finished second - a distant 16.8 seconds behind the Red Bull driver - after starting ninth.
Vettel seized the lead from Mercedes' pole-sitter Lewis Hamilton on the Kemmel straight after Eau Rouge and never looked back while threatened rain held off. The German now has 197 points to Alonso's 151."It was a fantastic race for us from start to finish really," he said after his 31st career win.
Britain's Lewis Hamilton, winner of the previous race in Hungary and on pole for the fourth race in a row, took third place for Mercedes ahead of team mate Nico Rosberg and moved up to third overall on 139.
Kimi Raikkonen's run of 27 successive races in the points came to an end with the first retirement since his comeback last year.The Finn had started the day second in the championship but fell to fourth overall with 134 points after pulling into the pits and stopping with what looked like a brake problem.
The race, on one of the fastest and most challenging circuits on the calendar, was no thriller and the outcome proved a disappointment for those fans who had hoped to see Vettel slowed on his march to a fourth successive title.
"Today it was a little bit boring, we get second place but no threat to Sebastian Vettel and had no threat from behind," said Alonso, whose team's home Italian Grand Prix is next up. "It is an important weekend for us and the team and we arrived fully motivated and in Monza we would like to give some smiles to our fans."