South Africa was all out for 274 on the fourth day at the Wanderers, way off the huge target of 466.
The home team didn't come close as England took two wickets in the first session, two right at the end of the second, and then ran through the rest of South Africa in dominant fashion to win with a day to spare.
Joe Root said through the series that victory would be the most significant in his three-year reign as England captain. He has what he wanted.
Yet a month ago, England was 1-0 down in the series, struggling to recover from a flu-like virus that swept through the squad, and rocked by series-ending injuries to opening batsman Rory Burns and fast bowlers James Anderson and Jofra Archer.
The turnaround was incredible. England won three tests in a row, all by big margins.
"Very special indeed," Root said. "It's taken a lot. Obviously you look at the first game and where we were there, and to pick ourselves up and play the way we have done in the last three games is extremely pleasing. It's taken a big effort from everyone."
The margin of victory in the series was also significant. It's the most convincing performance by an England team in South Africa since England won a five-test series 4-0 in 1914, six months before the outbreak of World War I.
Mark Wood was England's bowling star with 4-54 in the second innings and nine wickets in the match, his second test of an impressive return after being out of the team with injury for nearly a year.
Bowling fast, Wood clinched it with the wicket of Anrich Nortje, caught behind by wicketkeeper Jos Buttler. The decision didn't immediately go England's way but the tourists reviewed and TV replays confirmed their triumph.
The England players were already celebrating in the Johannesburg sunshine anyway.
Wood wasn't even meant to play but Archer pulled up with a recurrence of his elbow injury in the warmup at the Wanderers and Wood was called back in.
"Boy am I glad I played now," Wood said. "I'm over the moon."
Star allrounder Ben Stokes proved his worth on the final day, as he's done all series, with crucial breakthroughs to get rid of stubborn South Africa opener Dean Elgar (24) and captain Faf du Plessis (35). The wicket of du Plessis broke South Africa's most meaningful partnership.
Du Plessis and Rassie van der Dussen put on 92 in a period of fight from the home team after lunch but England removed both in the space of an over on the brink of tea and surged to victory from there.
Stokes roared in and his delivery kept low to bowl du Plessis.
Van der Dussen was out for 98 to Wood to miss his chance of a maiden test century in his debut series.
That double blow knocked the resistance out of South Africa. England finished it off effectively, taking the last seven wickets for just 87 runs.
Stokes made 318 runs in the four tests, with one century and a half-century, and took 10 wickets and collected plenty of sharp catches at second slip. Another high-quality showing earned him the man of the series, during which he was crowned international cricketer of the year.
"It's always such a competitive series," Stokes said. "I just think I really enjoy the competition that South Africa always brings."
Van der Dussen's exit was the beginning of the end but Stuart Broad produced the ball of the day, a fierce, rising delivery in the direction of Temba Bavuma's throat that Bavuma gloved behind. De Kock went down swinging, hitting six fours and a six before Wood forced him to mistime one.
There was a nice moment when South Africa seam bowler Vernon Philander was out. It was Philander's final test before retiring from international cricket and he'd been struck down by a right hamstring tear the day before. He still came out to bat and England players lined up to shake his hand as he walked off.
The series also had fiery moments; Four players, including Philander and Stokes, were fined for swearing at opponents — or in Stokes' case a fan — or for provocative wicket celebrations. Du Plessis and Broad had a verbal confrontation on the last day.
"We all obviously fight hard on the park but at the end of the day we remain gentlemen," Philander said, appreciating England players' efforts to congratulate him on his career.
This tour was dubbed England's 'Tour of Hell' at the beginning because of the illness and injury woes but it's turned out to be heavenly, with triumph and the emergence of a new breed of youngsters that contributed heavily to the success.
"The sky's the limit right now," Root said. "I do think we are very much at the start of something and we've got to look to keep learning to keep getting better."