Both Londoner Barker and Australian champ Geale are renowned for their work rates and put them on display in a gruelling 12-round war.
There was hardly anything between the two men in 11 of the dozen rounds, but Barker somehow escaped a stoppage defeat in the sixth when he was put down by a killer liver hook from Geale.
Staggering up at the count of nine, Barker went on to finish the three-minute period on top before opening up an advantage heading towards the final round by out-hustling and counter-punching the increasingly-frustrated titlist.
The 'Dazzling' one almost found himself in peril once more in the final round as Geale unloaded with several crisp shots to the head and body, but the Englishman stayed on his feet and made his way to the judges' scorecards which read 116-111, 113-114 and 114-113 in his favour.
An elated Barker, who missed over a year of action after a late knockout loss to Sergio Martinez in his first world title opportunity, dropped to the canvas in tears at the decision before embracing the dozen fellow fighters who came out to support him, and promoter Eddie Hearn.
The Eurosport-Yahoo! scorecard had Barker ahead 114-113.
Barker dedicated the win to his brother Gary, also a talented boxer who died in a car crash seven years ago, and said he was the inspiration behind his remarkable fightback having been knocked down.
"Not many people know the journey I've been through," the new champion said after the bout. "I dedicate this to my late brother Gary, this is for you.
"I knew there wasn't much in it. I want to go home now and see my daughter. Before I do that, there might be a few beers consumed!
“I take my hat off to Daniel Geale. He's a great champion and just a tough, tough man. When I was knocked down I thought of my brother and everyone who stuck by me and I got up.
"I was in absolute bits, I won’t lie. But their faces came into my head and it made me get up.
"It was the only round that made the fight close, though. I showed my heart and my power in the rest of the fight.
"Thank you to all the English fans who came out here."
Geale felt he had done enough to win what was a fantastic, close contest, but remained philosophical after losing his title.
He said: "I won't whinge and cry. It didn't go my way so I am very disappointed. I put everything into that fight, my whole body. I hurt him throughout the fight so I am disappointed.
"I could tell he was throwing a lot. Whether they caught me is another story, but I felt a lot were them were glancing and on my gloves. It wasn't my best performance but Darren is a great performer. It was a close fight and I am disappointed."
There was another world title changing-of-the-guard in the chief support bout, with Kiko Martinez - the Spaniard earlier this year stopped by Northern Ireland's Carl Frampton - surprising IBF super-bantamweight titlist Jhonatan Romero of Colombia with a superbly-relentless onslaught from the offset for a sixth-round stoppage.
The title win, albeit deserved on the night, comes as a surprise after Martinez's European title loss to 'The Jackal' in Belfast and will give Frampton extra belief that he will one day be a world champion himself.