Boris Johnson gave his last speech as prime minister by saying: "This is it, folks", before departing No 10 for Balmoral to officially offer his resignation to the Queen.
Liz Truss has now been confirmed as prime minister by the Queen.
Speaking outside Downing Street, Johnson sought to highlight what he views as his government’s successful record on Brexit, supporting Ukraine and the COVID vaccine rollout.
Watch: 'This is it, folks!', Boris Johnson gives final farewell as he leaves office
Boris Johnson has complained the rules were "changed" as he gave his final address as prime minister outside Downing Street.
The Conservative Party announced Liz Truss as his successor as leader on Monday after beating former Chancellor Rishi Sunak.
Speaking to a crowd outside Downing Street, Johnson sought to highlight what he views as his government’s successful record on Brexit, supporting Ukraine and the COVID vaccine rollout.
He also made a bitter jibe at the MPs who ousted him, forcing him to resign three years after winning a general election.
He claimed "they changed the rules" during his premiership, but did not specify how.
“The baton will be handed over in what has unexpectedly turned out to be a relay race – they changed the rules halfway through, but never mind,” he said outside No 10.
Tory MPs and officials who had gathered to watch laughed as he compared himself to a “booster rocket” jetting off into distant lands as he resigned his post - in a sign he will be taking a step back from frontline politics now he is no longer PM.
He also said he would be offering “fervent support” to Truss’ government during a “tough time” for households across the country.
There was no mention of Partygate, which has blighted his premiership and saw him become the first sitting prime minister to be fined for breaking the law, or of the litany of scandals which ultimately saw his own Cabinet members turn against him and lead to his resignation.
Johnson acknowledged rumours of infighting within the Conservative Party ranks and said if his dog Dilyn and Larry the cat can “put behind them their occasional difficulties”, then so can the Tory party.
He said: “Thank you to everybody behind me in this building. Thank you to all of you in Government. Thank you everybody who’s helped look after me and my family over the last three years, including Dilyn the dog.
“I just say to my party if Dilyn and Larry can put behind them their occasional difficulties, then so can the Conservative Party.
Truss has already begun preparations for her new cabinet as she heads into an extremely busy few days.
A number of key allies and supporters have already been pencilled in for some of the most senior roles, including Business Secretary Kwasi Kwarteng who is widely expected to be given the crucial role of chancellor.