Boris Johnson, Tory party leader, has stated that it was "painful" not to be able see through so many ideas and projects.
As he resigned, the PM was greeted by his family and staff outside No 10.
He claimed he tried to convince colleagues that it would be "eccentric to change leaders" and blamed Westminster's "herd instinct" for his departure.
He stated that he would continue to serve in the office until his successor is elected.
He said that a timetable for the leadership contest would be released next week. The next UK prime minister will be the winner of this contest.
Johnson, however, is being urged to immediately leave No 10, including Sir John Major, the former Conservative prime minister.
Sir John wrote to party leaders, urging them to speed up the leadership contest or, if necessary, for deputy PM Dominic Raab to take over as caretaker PM.
After a massive revolt by ministers against Johnson's leadership, which was sparked on Tuesday by the dramatic resignations of Health Secretary Sajid Javid and Chancellor Rishi Sunak, Mr Johnson resigned.
For 48 hours, he resisted the calls to quit, including those from Nadhim Zahawi, newly appointed Chancellor. It was then that it became obvious that he had lost confidence in his party and couldn't continue.
Outside Downing Street, he stated that he had won an "incredible mandate", winning the largest Conservative majority since 1987, and that he was now in a position to secure it again.
"The reason why I have worked so hard over the past few days to continue to deliver this mandate in person was not because I wanted to, but because it was my duty, my obligation, and my job to do what I promised in 2019.
He said that he regretted not being able to win those arguments, but acknowledged that his party's will was "clear".
He said, "In politics no one is remotely indispensable."
He stated that he was proud to have been elected, and cited the UK's exit from the EU, the government response to Covid, and the rollout of the vaccine program.
He stated that he was the leader of "the West" in resisting Putin's aggression against Ukraine.
He addressed the Ukrainian people and said that the UK would continue to support their fight for freedom as long as it took.
President Volodymyr Zelensky praised Johnson for "realising and being at the forefront [of support] Ukraine"
Johnson thanked Carrie, his wife, and their children, as well as Downing Street staff and "you, British people" for the enormous privilege they have given him.
He said, "I know that even though things may seem dark at times, our future together will be bright."
He said that he and his Cabinet would serve the nation's interests until a new leader was chosen. His cabinet has been reconstituted, and they will meet again later.
However, he still has to replace the many junior ministers from several departments who quit in order to force his departure.
In July 2019, Mr Johnson was elected to power and, six months later, he won a large majority in a general elections.
He has been plagued by controversy in recent months. This includes a fine for violating his lockdown laws and his handling sexual misconduct allegations against Chris Pincher, former Chief Whip.
The speech of the PM was short. However, his departure from office will not be immediate.
He wanted history to understand that his resignation was not his fault, but the fault of his colleagues. He called the "herd" and said it had moved quickly despite having the largest majority in the 2019 general elections since 1987. It also attracted new voters to his party.
The idea is that the coalition of voters, including Labour supporters, he gathered in 2019 could fall apart without him keeping it together.
He mentioned the negative press he received in recent weeks, but didn’t dwell on any of his mistakes while in office that led to mass resignations and a vote against confidence.
He just acknowledged that he had not persuaded his colleagues to let him stay in office.
He will continue until a new leader is elected. However, it is the backbench committee 1922 that will determine the timeline. Some MPs want it to be expedited so he does not remain in office until the autumn.
He doesn't seem to be in any hurry to go now that he has new cabinet ministers. He wants a legacy that isn’t tarnished by the chaos of the past few days.
To replace the leader who is leaving, the Conservative Party will hold a leadership contest.
Attorney General Suella Braverman has been the Tory MP who has so far declared she will stand. Steve Baker said that he is seriously considering running.
More candidates are expected to join them in the coming days, although deputy PM Dominic Raab has ruled him out.
Some Conservative MPs have also expressed concern that Johnson would remain in office until autumn. One said Johnson had lost "the trust & authority necessary to continue".
Sir Keir Starmer, Labour leader, said that Mr Johnson must resign immediately and warned him that Labour would vote no confidence in the government at Parliament.
The government losing the confidence vote could result in a general election. However, to pass the motion, many Conservative MPs would need to support it.
