Home secretary Theresa May and secretary of state for justice Michael Gove had already declared their intention to run.
Boris Johnson has ruled himself out of the race to become the next Prime Minister.
Home secretary Theresa May and secretary of state for justice Michael Gove had already declared their intention to run.
Johnson said: “Having consulted colleagues and in view of the circumstances in parliament I have concluded that person cannot be me.
“My role will be to give every possible support to the next Conservative administration to make sure we properly fulfil the mandate of the people that was delivered with the referendum and to champion the agenda I believe in.”
The other Tories standing for leadership are leave campaigner Liam Fox, secretary of state for work and pensions Stephen Crabb and minister of state for energy Andrea Leadsom.
MPs will vote for their next leader next Tuesday in a secret ballot and the candidate with the fewest votes will be eliminated.
Voting will take place every Tuesday and Thursday until the list of candidates is whittled down to two.
Gove stuck the boot into Johnson earlier today, whom he was expected to support.
He said: “I wanted to help build a team behind Boris Johnson so that a politician who argued for leaving the European Union could lead us to a better future.
“But I have come, reluctantly, to the conclusion that Boris cannot provide the leadership or build the team for the task ahead.”
Theresa May said: “Following last week’s referendum, our country needs strong, proven leadership to steer us through this period of economic and political uncertainty, and to negotiate the best possible terms as we leave the European Union.
“Some need to be told that what the government does isn’t a game, it’s a serious business that has real consequences for people’s lives.”
