Galahad won his all-British bout with Jazza Dickens in Essex when the fight was stopped after 11 rounds.
The 31-year-old from Sheffield, who was born in Doha dominated the Brentwood contest and referee Michael Alexander called a halt to proceedings with Dickens badly cut around the eye.
Galahad’s victory was the second of his career over Dickens and earned him a world belt two years after a controversial defeat to Josh Warrington in Leeds.
Galahad was in control of the fight for many of the rounds and, while Dickens fought on bravely, injuries forced the abandonment of the contest at the end of the 11th.
“It’s unbelievable,” said Galahad. “After 19 years of hard work, blood and sweat I’ve finally got the IBF belt round my waist.
“I have had 18 months out and I have just smashed a future world champion from pillar to post.
“I moved home at 15, into a crappy flat next to the gym with five other boxers with rats running around the floor, and now I am a world champion and I can get my mum a nice house.”
It is Galahad’s first world title win in his 29th bout as a professional.
Former champion Warrington had given up the title in January after holding the belt since May 2018. Galahad’s only previous world title fight ended in a split-decision points defeat against Warrington in 2019.
That night Galahad was left fuming after a title fight he felt he had won.
On Saturday he showed he had learned from that when his second chance came around.
“I didn’t want to leave it to the referees or judges,” he said. “Now I want to win a couple more titles and unify the division. If I fight Warrington, he’s not going 12.”
Warrington is next in action on September 4 at Emerald Headingley when he meets Mauricio Lara in a rematch of the fight in February in which the Leeds Warrior suffered his first defeat.