In beating four-times champion John Higgins 18-15, Selby joined an elite group of just three players to have won back-to-back titles at the Crucible.
The world No 1 was stunned when underdog Higgins romped into a 10-4 lead, before reeling off nine of the next 10 frames to actually lead 13-11 on Sunday afternoon.
Selby returned this evening and had to hold off a mini recovery from Higgins, who reduced the gap from 16-12 to 16-15, before getting his hands on the famous trophy - and £375,000 top prize - in Sheffield.
"I can't believe it, I am still pinching myself now," said Selby. "From 10-4 to get to 10-7 yesterday, I was over the moon as I had nothing left. He outplayed me yesterday. Today I came back fresh and was a lot better.
"When I was 10-4 down I was missing everything and had nothing left. I said 'pull something together'. If you lose, you want to at least go down fighting."
"Big congratulations to John, he is a great guy, and one of the all-time greats and it is so great to play him in another final. To have three world titles is unbelievable and to be one of only four players to defend it is something I could only dream of."
When it comes to sporting fightbacks, Sheffield golfer Danny Willett - in the Crucible crowd yesterday - has his own chapter in the history books.
Last year, he overhauled Jordan Spieth’s five-shot advantage to be crowned Masters champion at Augusta.
But, this was different. Spieth capitulated with that crazy run of shots at the par-three 12th, where he twice found the water on his way to a quadruple bogey seven.
At the Crucible, Higgins was helpless as Selby showed the match-play snooker qualities which have seen him occupy the world No 1 spot for the last two years.
The 33-year-old - who won the title three times in four years, after triumphs in 2014 and 2016 - was looking to join Steve Davis, Stephen Hendry and Ronnie O’Sullivan as the only players to have successfully defended their Crucible crown.
And, Selby has previous, having battled back from 10-5 down against O’Sullivan in that 2014 final.
Selby will pinpoint Sunday night’s final three frames which gave him the platform for this victory.
Trailing 10-4, it looked terminal, but somehow he raised his game, breaks of 81 and 121 helping to cut the deficit to 10-7 overnight.
And the Leicester potter returned today, winning six of the seven frames played to leave Higgins shell-shocked.
After a scrappy opener, frame 19 saw all remaining 12 reds scattered over the baulk end, Selby pounced after Higgins missed a long-range attempt.
At 10-9, Higgins needed to respond, but three failed attempts to escape a snooker - hitting the brown each time to pot the white ball - looked ominous.
The 41-year-old - looking to become the oldest Crucible champion since 45-year-old Ray Reardon triumphed in 1978 - managed to eke out a 78 to briefly stop the rot.
Selby came out on top after a 45-minute frame, and then reeled off frame-winning breaks of 67, 58 and 72 to edge 13-11 in front.
The last time the pair met in a Crucible final - 10 years ago in 2007 - it was Higgins who came out on top.
But Selby had the scent of revenge in his nostrils yesterday, the pair trading the first two frames of the evening.
It was a low-scoring final, match-play attrition rather than eye-catching centuries, but breaks of 71, 54 and 70 saw Selby pull away to 16-12 heading into the mid-session interval.
The interval was a welcome break for Higgins, who first won the World Championship 19 years ago in 1998.
That experience - he made his Crucible debut in 1995 - was vital as he returned composed, free of the earlier shackles, to win the next three frames - thanks to breaks of 88, 111 and a gritty 43 - to cut the gap to 16-15.
The last of those saw referee Jan Verhaas intervene to call a foul on a disgruntled Selby, who thought he had hit the black as he attempted to roll up for a snooker. Television replays proved inconclusive, so the experienced Verhaas stuck to his decision.
It was a decision which could have upset less experienced players, but Selby was unruffled. He fired in a tremendous long-range red, going on to clear the table with a 131.
After winning four ranking titles this season - the Paul Hunter Classic, International Championship, UK Championship and China Open - Selby has dominated in 2016-17.
But this was his toughest Crucible final, to date, after coming through 18-14 against Ronnie O’Sullivan in 2014 and Ding Junhui 12 months ago.
A 131 clearance, initiated with a superb long-range red, nudged Selby towards the finishing line, at 17-15, before completing his remarkable comeback - firing in a 75 break - to master the Crucible once more.
Higgins said: "Mark is granite, just granite. In the second session I had my chances, I missed a pink into the middle bag and I could have gone 9-3 ahead.
"That was a big, big frame. Mark cleared up under extreme pressure. He is a fantastic champion.
"It has been an unbelievable tournament, I gave everything. I came up short to a great champion. I'm proud of myself but he was too good on the day."