Boris Johnson has pulled out of the Conservative leadership race, Sky News has reported.
His withdrawal leaves the path to No 10 open to Rishi Sunak.
The former prime minister had the public backing of 59 Tory MPs but had to reach 100 to proceed in the race.
Mr Sunak, the former chancellor, has more than 140 backers, a significant lead over Penny Mordaunt, the only other remaining candidate. If he wins, Mr Sunak will become the third prime minister this year.
In a statement, Mr Johnson said he had “cleared the very high hurdle of 102 nominations”, but came to the conclusion that “this is simply not the right time”.
He said he had “reached out” to leadership rivals Mr Sunak and Ms Mordaunt to see if they could work together in the national interest, but it had not proved possible.
He added that although he was “attracted” to run because of the support from his colleagues, “you can’t govern effectively unless you have a united party in parliament”.