Tony Blair has stood down as UK prime minister after 10 years in the job.
He handed in his resignation to the Queen during a private meeting at Buckingham Palace.
Earlier, Mr Blair received a standing ovation from MPs in the Commons in unprecedented scenes at the end of his final prime minister's questions.
Conservative, Lib Dem and DUP leaders all paid tribute to Mr Blair, who is expected to stand down as an MP to take up a job as a Middle East envoy.
He will stand down later as an MP before taking up a new job as a Middle East peace envoy for the "quartet" of the UN, EU, America and Russia.
As they left Downing Street the Blair family - including their four children - posed for the gathered world media.
Mr Blair said nothing to the press as they got in the car, but wife Cherie smiled and waved at the press and said she would not "miss" them.
Earlier MPs from all sides called a halt to the usual House of Commons hostilities to pay tribute to him during Mr Blair's final half hour question time session.
Mr Blair admitted he had "never pretended to be a great House of Commons man" but he paid tribute to the "noble" work of MPs and - in his final words to Parliament - said: "I wish everyone, friend or foe, well and that is that, the end."
MPs gave departing Mr Blair a standing ovation
Mr Blair, who was being watched from the public gallery by his family, also paid tribute to troops killed in Iraq.
He hailed Britain's armed forces as the "bravest and the best" and said he was "truly sorry about the dangers they face today in Iraq and Afghanistan".
He added: "I know some people think they face those dangers in vain. I don't and I never will.
"I believe they are fighting for the security of this country and of the wider world against people who would destroy our way of life."
Conservative leader David Cameron hailed Mr Blair's "remarkable achievement" in being prime minister for 10 years, praising peace in Northern Ireland and Mr Blair's work in the developing world which he said will "endure".
He wished Mr Blair "every success for whatever he does in the future".
HOW THE DAY UNFOLDED
1200 - 1230: Final PMQs
1300: Blair says farewell to staff at No 10
1312: Blair arrives at Palace, where he tenders resignation in private audience with Queen
1330: Brown departs Treasury with wife Sarah
1340: Blair leaves Palace
1351: Brown arrives at Palace where Queen asks him to form a government
1448: Brown leaves Palace
1455: Brown enters No 10 for first time as prime minister
Mr Blair thanked Mr Cameron for his tributes and said although he could not wish the Tory leader well politically, "personally I wish both him and his family very well indeed".
Lib Dem leader Sir Menzies Campbell said that, despite their political disagreements, Mr Blair had been "unfailingly courteous" and extended his party's best wishes to the outgoing prime minister and his family.
Mr Blair returned the compliment, saying Sir Menzies had a "generosity of spirit and courtesy".
Mr Blair also exchanged tributes with Northern Ireland first minister Ian Paisley.
To laughter from all sides, Mr Blair told MPs he had received his own P45 on Tuesday.
Asked by Lib Dem MP Richard Younger-Ross to advise his successor Gordon Brown on the relationship between faith and the state, Mr Blair sparked more laughter by saying, after a brief pause: "I think I'm really not bothered about that one."
Looking ahead to his new role, Mr Blair told MPs he believed a solution could be found in the Middle East but it would take a "huge intensity of focus and work".
He told MPs: "As I learned in respect of Northern Ireland, it is important to be able to bring people together, including people who have been very hostile towards each other."
Mr Blair is travelling to his Sedgefield constituency, in the north east of England, where he is expected to announce he is standing down as an MP with immediate effect after 24 years.
John Prescott is also stepping down from frontline politics after 10 years as deputy prime minister. It is not certain whether Mr Brown will appoint a replacement.
Mr Brown is thought likely to carry out the bulk of his Cabinet reshuffle on Thursday, but it has already emerged that one definite change will see Patricia Hewitt stepping down as health secretary.