Warrington overwhelmed Selby and short odds in favour of the Welshman with a relentless display in front of a huge Elland Road crowd, cutting Selby early on and beating him on a split points decision.
Selby, who was making the fifth defence of the belt he won in 2015, struggled to cope with Warrington’s intensity and was rocked on several occasions as he fought to recover from a bad start which left blood streaming from his left eye midway through the second round.
Warrington celebrated at the final bell and he and Selby - bitter adversaries for the past two years - shared some mutual respect but a crowd of 20,000 were incredulous as Canadian judge Andrew Davis scored the fight 115-113 in favour of Selby.
The two remaining judges, however, gave the victory to Warrington as the 27-year-old claimed a world belt in his 27th professional fight.
“I could die a happy man now, I really could,” Warrington said. “I couldn’t put it into words. What an occasion, what a night. It’s a fairytale ending.
“I’ve been doubted for a very long time. I was doubted at English level, I was doubted at British level. I wasn’t meant to go any further. But number one in the world. No-one would ever have thought I’d got the speed, the punching power or the boxing intelligence but I outboxed, outfought and outsmarted a brilliant champion in Lee Selby.”
Warrington, a Leeds United fan and season-ticket holder, has repeatedly stated his ambition to fight for a world title at Elland Road and promoter Frank Warren realised that dream by securing the venue in January.
The Kaiser Chiefs warmed up the crowd with a set before the clash with Selby and Warrington was joined on his ringwalk by former Leeds captain Lucas Radebe, who flew in from South Africa.
Warrington said the atmosphere inside Elland Road had helped to cure a sudden crisis of confidence in the hours beforehand.
“I’ve always been confident throughout the build up to the fight, in the press conferences and the open workouts,” he said. “I’ve always massively believed that I had this fight won.
“But earlier today I just got hit by a massive wave of nerves. I started thinking ‘what if it’s not meant to be. I’ve got the expectation of a whole city on my shoulders.’ As soon as I got into the venue tonight, it all lifted. As soon as I got in that ring and looked about I thought ‘there’s no way I’m losing this fight.’ The proof’s in the pudding.”
Warrington and Selby have had an acrimonious relationship since a mooted meeting between them fell through two years ago fell. Selby accused Warrington of “bottling” the fight. Warrington said he had merely wanted a new date to allow him to get married that summer.
The pair were involved in several bitter exchanges in the lead up to this weekend’s clash but Warrington attempted to end their feud, saying: “Prior to this fight I always had respect for Lee because it takes a good fighter to win world title and defend it more than one occasion.
“He took it personal a few years ago and naturally I'm a lad from an estate so I responded. There was a lot of animosity in the build-up and in the last week but I said to him after the final bell ‘what’s done is done. We’ve just had 12 rounds to sort it out.’ Hopefully we’ll leave it at that.”
In a statement released on Twitter this morning, Selby congratulated Warrington but said the fight would be his last at featherweight after a battle to make the nine-stone limit.
"I was Britain's longest reigning world champion but it came as a price," Selby wrote. "I've been making the featherweight limit for 10 years but it was one fight too many and my performance badly reflected that. Congratulations to Josh and I wish him the best in the future."