The One Direction heartthrob popped the question to a lucky supporter who was dressed as a bride at the 'Little Things' hitmakers' gig in Philadelphia on Wednesday (13.08.14) after he picked her out of the sell-out crowd and joked he didn't want her efforts to go to waste.
While the boy band were thanking the audience at the end of their gig, Harry said: "I heard there was a girl here in a wedding dress ... is there a girl here in a wedding dress?
"Now I feel bad letting this go to waste so what's your name? Preeya? Preeya ... will you marry me? There's been a plot twist! OK .. awesome."
The 20-year-old singer then joked that he and his new love were going to wait until everyone had sent them presents to celebrate their engagement before calling it off.
He added: "We'll take the engagement gifts and then we'll ... OK, awesome. I almost wore my wedding dress. It could've been awkward. But that's a different story."
Ladies man Harry has had several failed high-profile relationships with stars including Kendall Jenner, Caroline Flack and Taylor Swift.
Taylor appeared to make a dig at Harry - who she split from in January following a brier romance - at the Teen Choice Awards on Sunday (10.08.14) when she made a cheeky quip while introducing the Choice Actor in a Drama Movie category.
Speaking to the audience, the 24-year-old beauty said: "Oh, hey guys. You know we've had some amazing memories here together at the Teen Choice Awards.
"And so, I was excited when they asked me to come and present this award, because no one knows more about dramatic males than I do."