It's not actually unusual for a British prime minister to enter power like this. But does Johnson need a mandate more than most?
Parliamentarians and party members have held their noses and voted in a man deeply unsuited to lead. Now the British public must live with their choice.
Two leadership experts weigh up the characteristics of the Conservative Party leadership hopefuls.
In keeping with the permanent state of political misery induced by Brexit, any outcome of the leadership contest and the subsequent UK-EU politics will make almost everyone unhappy.
The favourite to become the next prime minister has never felt the need to apologise for his offensive remarks about Muslim women.
Conservative members will now vote on which of the two candidates will become their party leader – and the prime minister.
If the Conservative MP was really a spook, he wouldn't be the first to make the leap into parliament.
At the start of this election, party members said they wanted to avoid another 'coronation', so why is the lead candidate being allowed to avoid scrutiny?
Johnson is the least popular among women MPs and Jeremy Hunt managed to get a vote from the European Research Group.
Snubbed for a recent state dinner with Donal Trump, the home secretary walks a difficult line in a party struggling with the question of islamophobia.
Rory Stewarts unconventional style has landed him in the second round of the Conservative leadership election – but he spins like a classic politician.
The speed is about to pick up as the field narrows.
Brexit will inevitably dominate this campaign, but the next prime minister also needs positions on austerity, party unity and how to actually survive in parliament.
Study suggests certain psychological characteristics get you to the frontbench. But they might not make you many friends along the way.
Party members who support the former London mayor's leadership bid describe themselves as very right wing, even by Conservative standards.
It's hard to say if, legally, not paying the Brexit bill will classify as a sovereign default. But credit agencies will take serious notice.
The party does have younger members, but their voices are not being heard as the leadership contest gets underway.
It's a strategically poor choice – and that's no coincidence.
Boris Johnson's attitude to Brexit and business has traders on high alert.
Boris Johnson, Amber Rudd, Dominic Raab? Who will be the next prime minister?