Hamilton crossed the line 20.5 seconds ahead of teammate Valtteri Bottas, giving a hint that Mercedes and Hamilton could be back to their dominant ways. He joined seven-time champion Schumacher and two-time champion Finn Mika Hakkinen as a three-time victor in Spain.
Vettel remained within sight of third-placed Max Verstappen throughout the remainder of the race but was unable to find a way past.
"As everyone knows, it's extremely hard to overtake here, and I could always put pressure on him when we needed, but you need such a big gap between the [two cars'] pace to get through".
It marked the third time he has been in the gravel this weekend.
"That's more like it guys, great job", said Hamilton on team radio.
"People probably think it was an easy race and I was cruising but I wasn't cruising", he explained.More news: STDs reach all-time high in California
It looked like it would be a challenging race for Hamilton when Vettel jumped Bottas on the first lap, but two safety cars and some poor strategy resulted in the German finishing fourth.
But Vettel struggled with tire wear and Ferrari chose to bring him in for an extra stop.
A first pole position since March on Saturday was followed by a peerless show of front-running from the Englishman on Sunday, particularly in the opening stint when Hamilton pulled away from Vettel by in excess of half-a-second per lap. Therefore we were not able to stay out for another 23 laps.
"We couldn't make the tyres last, so for us it was clear we come in again".More news: Andy Samberg wants celeb fans to guest star on 'Brooklyn Nine-Nine'
Such was Lewis Hamilton's advantage in Sunday's Spanish GP that the Brit says he used the race as a "test bench" to better understand his W09. One of them was Haas driver Romain Grosjean, who spun his auto following the start into Turn 1, collecting Nico Hulkenberg and Pierre Gasly, which put all three out of the race with sufficient damage.
Grosjean, who struggled throughout the weekend, couldn't stop his auto from spinning across the track on Turn 3 and Hulkenberg and Gasly could not avoid colliding with him. Grosjean was later handed a three-place grid penalty for the next race in Monaco.
But their current line-up of Lance Stroll, the Canadian teenager whose career has been bankrolled by his fashion billionaire father Lawrence, and Russian Sergey Sirotkin, is possibly the worst in the team's history. Luckily for Verstappen, the damage was only to his front wing endplate and didn't limit his performance too much.
"Feels nice to be on the podium and nice to have a good clean race", said Verstappen. "Kimi (Raikkonen) had an issue with the engine yesterday, had to change the engine today and obviously retired in the race". Renault managed to turn his auto around in time to attempt a final run, but he finished the session 16th - just 0.04s slower than Stoffel Vandoorne.
Teams will stay in Barcelona for two days of testing at the Circuit de Barcelona-Catalunya.More news: Petrol, diesel prices start buzzing soon after Karnataka elections