The YouGov/Times poll showed the Labour leader on 35%, ahead of the Prime Minister on 34%. Nearly a third (30%) said they were unsure.
It comes with Mrs May under intense pressure following a disastrous general election in which the Tories lost their majority and her authority was severely diminished after her highly personal campaign appeared to backfire.
In the days before the vote (June 5-7), Mrs May was ahead on 43% to Mr Corbyn’s 32%, suggesting the aftermath of the election, in which the PM has been criticised over her response to the Grenfell Tower disaster, may have had an effect.
Mrs May has also been forced to ditch a number of unpopular manifesto promises from her first Queen’s Speech, which set out the Government’s legislative agenda for the next two years.
Mr Corbyn used his response to the Queen’s Speech in the House of Commons to claim Labour is now a “government in waiting”, although he was mockingly praised by the PM for having “fought a spirited campaign and come a good second”.