Johnson, a former London mayor, was also a leading voice in the “Vote Leave” movement on the referendum to leave the European Union. “Leave” won with 52 percent of the vote last week.
Johnson said he was not the right person to unite the country as it exits the EU.
“Having consulted colleagues and in view of the circumstances in Parliament, I have concluded that person cannot be me,” he told reporters. “My role will be to give every possible support to the next Conservative administration, to make sure that we properly fulfill the mandate of the people that was delivered at the referendum, and to champion the agenda I believe in.”
His decision came shortly after Justice Secretary Michael Gove — an ally of Johnson who had been expected to back him in the race — announced that he would run.
In announcing he would run, Gove politician conceded that he has “repeatedly” said before that he did not want to be prime minister. But he said he decided to seek office over concerns that Johnson would not be able to lead the country in the wake of the Brexit decision.
“I have come reluctantly to the conclusion that Boris [Johnson] cannot provide the leadership or build the team for the task ahead,” Gove said. “I have, therefore, decided to put my name forward for the leadership. I want there to be an open and positive debate about the path the country will now take.”
Gove now joins a race with five other candidates, including Home Secretary Theresa May, Minister Andrea Leadsom, MP Liam Fox and Work and Pensions Secretary Stephen Crabb.