He spoke from a lectern outside 10 Downing Street on Thursday afternoon (July 7).
Mr Johnson announced his intention to remain in office as interim prime minister until his successor is decided.
What did the Prime Minister say in his announcement and why did he resign?
“Good afternoon everyone. Good day, thank you, thank you.
“It is now clearly the will of the parliamentary Conservative Party that there should be a new leader of that party and there should be a new prime minister.
“And I have agreed with Sir Graham Brady, the leader of our backbench MPs, that the process of electing this new leader should start now and the timetable will be announced next week.
“And I appointed a cabinet today to serve as long as I want until a new leader is in place.
“I want to say that to the millions of people who voted for us in 2019, many of whom voted Conservative for the first time.
“Thank you for this incredible mandate, the largest Conservative majority since 1987, the largest share of the vote since 1979.
“And the reason why I have fought so hard over the last few days to continue to personally fulfill this mandate was not just because I wanted to, but because I felt it was my job, my duty, my obligation to you, to continue to do what we promised in 2019.
“And of course I am immensely proud of the achievements of this government, from facilitating Brexit to managing our relationship with the continent for over half a century and reclaiming the power for this country to make its own laws in Parliament.
“To get us all through the pandemic, to deliver the fastest vaccine roll-out in Europe, to create the fastest way out of lockdown and, in recent months, to lead the West in fighting back against Putin’s aggression in Ukraine.
“And now let me say to the people of Ukraine that I know we in the UK will support your fight for freedom for as long as it takes.”
“And at the same time, we have advanced a huge investment program in infrastructure, skills and technology in this country, the largest in a century.
“Because if I have an insight into the people, it’s the genius and the talent and the enthusiasm and the imagination that’s evenly distributed across the population but the opportunities aren’t and that’s why we have to keep improving and the potential in every part of the united states release kingdom.
“And if we can do that, we will be the wealthiest in Europe in this country.
“And for the past few days I’ve been trying to convince my colleagues that it would be eccentric to change governments when we’re doing so much and have such an extensive mandate and actually only a handful of them are points behind in the polls, even in the medium term after a few months of fairly relentless sleigh rides and when the economic situation at home and abroad is so difficult and I regret that I have not succeeded in these arguments and of course it is painful not to do so many ideas and projects myself to be able to see through.
“But as we saw at Westminster, the herd instinct is strong and when the herd moves, it moves.
“And my friends in politics, no one is remotely indispensable, and a brilliant and Darwinian system will produce another leader who is equally committed to moving this country forward through difficult times.”
“Not only to help families get through it, but to change and improve the way we do things.
“We need to unburden businesses and families, and yes, lower taxes, because that’s the way to generate the growth and income we need to pay for great public services.
“Under this new leader, I say, whoever he or she may be, I say I will give you as much support as I can.
“And for you, the British public, I know there will be many people who will be relieved and perhaps some disappointed.
“And I want you to know how sad I am to be leaving the best job in the world. But those are the breaks.
“I want to thank Carrie and our children and all of my family who have endured so much for so long.
“I would like to thank the unrivaled British Civil Service for all the help and support you have given, our Police, our Ambulance Services and of course the fantastic NHS who, at a critical moment, have helped extend my own tenure, our armed forces and ours world’s admired authorities and our tireless Conservative Party members and supporters, whose selfless work makes our democracy possible.
“I’d like to thank the wonderful staff here at Number 10 and of course the checkers.
“And by the way, our amazing Prop Force Detectives are the one group that never leaks.
“First and foremost, I would like to thank you, the British public, for the immense privilege you have given me.
“And I want you to know that from now until the new prime minister takes office, your interests will be served and the government of the country will continue.
“Being prime minister is an education in itself. I have traveled to every part of the UK and, alongside the beauty of our natural world, have found so many people possessed of such boundless British originality and so willing to tackle old problems in new ways that I even know that if things may seem dark at times now, our future together is golden. Many Thanks.
“Thank you all. Thank you.”
how can you watch
The resignation was broadcast live on BBC, ITV, Sky News and more.
You can watch the whole speech on YouTube.