The Frenchman crossed the finishing line after 1:44.67 just ahead of Poland’s Adam Kszczot. The Kenyan 19-year-old Kipyegon Bett was third.
It was France’s first gold in the event and the victory comes a year after 25-year-old Bosse finished fourth in the 800m in the Olympic final.
On a cold August evening in east London, Bosse took his destiny in his hands with 150 metres to go. He burst past Bett and race favourite Nijel Amos. “I am a gambler, I love going to the casino,” said Bosse. “And I just gambled. I put everything on the red.”
He added: “It felt like a nightmare as I was getting chased. I could not understand why nobody was going past me. Even when I crossed the line I could not believe it.”
Away from the track, Bosse is a keen guitarist and names the French songwriter Georges Brassens among his favourites. But any thoughts of poetry after his victory were soon suspended.
“On my lap of honour I saw my best friend in the crowd. He had a date with a girl in the south of France and we spoke to each other on the phone,” said Bosse. “He wished me the best of luck and I thought I’d see him again in France. And then I saw him in the crowd and I was so pleased.
“He came all the way from France to see me. Maybe he brought me luck. But a few hundred metres after seeing him I was throwing up. I cannot party like Usain Bolt.”