The prime minister told BBC Radio 4's Today she preferred "to get out and about and meet voters".
Her decision came on a day when ITV became the first broadcaster to confirm a debate ahead of the poll in June, announced by May yesterday.
A Number 10 source has told the BBC that the prime minister will not be changing her position, despite ITV's announcement.
Labour Party's Jeremy Corbyn accused May of "dodging" a head-to-head showdown and the Lib Dems urged broadcasters to "empty chair" her.
Corbyn said the PM's stance was "rather strange", adding: "I say to Theresa May, who said this election was about leadership, Come on and show some.'
"Let's have the debates. It's what democracy needs and what the British people deserve."
Liberal Democrat leader Tim Farron added: "The prime minister's attempt to dodge scrutiny shows how she holds the public in contempt.
"The British people deserve to see their potential leaders talking about the future of our country."
ITV is the first broadcaster to confirm a debate. No details have been released about the format or the date, but Julie Etchingham is expected to be the host, as she did in 2015.
A BBC spokesman said it was too early to say whether the broadcaster would put in a bid to stage a debate.
David Dimbleby, who hosted the BBC leaders' debates in both 2010 and 2015, said a refusal to take part in TV showdowns with her rivals could be "rather perilous" for May.
"I don't think other parties will refuse to take part in debates, and I wonder whether Number 10 will stick with that, because it may look a bit odd if other parties are facing audiences and making their case," he said.
They are a chance to hear, in a prime-time TV slot, what party leaders offer and how robustly they can defend their ideas, he said.
Prime Minister May's refusal may be seen by some "a bit chicken", BBC's Media Editor Amol Rajan said.
But why would she risk it, and give her opponents a formal platform at the same time, the Indian-origin journalist wondered.
Political leaders' TV debates featured in the last two general elections, in 2010 and 2015.
They took different forms at each - in terms of the line-up, questioning, topics and how they debated. A set of rules were thrashed out between party and broadcaster beforehand.
Viewer ratings in 2010 varied - from a peak of 10.3 million watching the first debate to 4 million for the second.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)