The 19-year-old did not describe himself as homosexual, saying "I still fancy girls," the BBC reported. But he said he is, at the moment, committed to a man.
"It did take me by surprise a little bit. It was always in the back of my head that something like that could happen," he said.
"But it wasn't until spring this year that something just clicked. It felt right and I thought 'OK.' And my whole world changed there and then."
Daley, who comes from Plymouth in Devon, said his friends and his family support him in the relationship.
Daley won a bronze medal at the London Olympics in 2012. He said he has not changed fundamentally.
"I mean I'm still Tom, I still want to win an Olympic gold medal in Rio 2016 for Great Britain," he said.