Excluded from school as a teenager, Toseef Khan had already been in prison four times by the time he was 19.
Just before he turned 20, he was sentenced to 16 years in prison for "gang-related offences" at Bradford Crown Court.
"I thought 'This is me f*****, what am I going to do?"
"I decided to turn my life around.
"In prison people coped in different ways, some turned to religion or meditation. I turned to education.
"I came out at 29 with a degree in criminology with the Open University. When I came out I thought 'I want to make up for the social harm that I've caused'."
Toseef was speaking at Elland Road, where Labour leader Sir Keir Starmer visited to speak to Leeds United Foundation's violence reduction unit, which helps young people to avoid a life of crime.
Now 38, Toseef mentors excluded children who go to pupil referral units like he did, as well as running his own organisation Shaping Future, Changing Lives, which aims to reduce the impact of crime on communities.
The key to getting through to vulnerable teenagers is to "level with them," he said.
"I come in looking professional and they look all big and bad."
"But when I tell them my experiences, they're taken aback
"They see I'm not any different to them. I tell them I've made the same mistakes they've made. My story is really effective."
His message to the young people he mentors is simple: "That life isn't worth it."
"You're never going to live like a kingpin. It's never too late to change," Toseef said.
"Sometimes those with the worst pasts create the best futures."
Toseef's comments came after the Labour leader spoke to the foundation's mentors about the violence reduction project.
He said the project's work with school pupils is crucial to ensuring children aren't pressured into crime.
"It's striking how much trauma they've experienced by the time they're 13 or 14," the Labour leader said.
Steve Hartley, who runs the violence reduction project for Leeds United Foundation, said the charity supports more than 1,000 vulnerable young people in Leeds to ensure they escape the clutches of crime.
Mentors visit schools and work one-to-one with excluded pupils, telling their own stories about their experiences with crime.
