Blair's June 27 departure means the mantle will likely pass to Gordon Brown, the rumpled architect of Britain's economic prosperity. Pilloried for everything from his dandruff to his alleged ruthlessness, Brown has long waited for the chance to emerge from Blair's shadow.
Blair won three straight terms as prime minister by banking on his common touch - a style that served him well as he returned to the northern England political club where he announced his campaign for Labour Party leader 13 years ago.
Visibly emotional, he struggled to keep smiling and offered a response to critics who have lambasted him for dragging Britain into the Iraq debacle.
"Hand on heart, I did what I thought was right," Blair told cheering and often tearful supporters. "I may have been wrong, but that's your call. But believe one thing if nothing else: I did what I thought was right for our country."
A pivotal moment in his decade-long reign came on Sept. 11, 2001, Blair said as he defended his stalwart relationship with the United States. Standing shoulder-to-shoulder with America earned him the admiration of two presidents.
President Bush described Blair as "a man who kept his word, which sometimes is rare in the political circles I run in." Bill Clinton praised Blair for taking the lead on climate change, debt relief for poor nations and aid for Africa, and for bringing peace in Northern Ireland and Kosovo.
In Blair's wake comes Brown, the prime minister's partner in pushing the Labour Party toward the center. Though Brown is expected to easily win election as the party's new leader and become the next prime minister, Blair has stopped just short of an open endorsement.
With Blair wounded by criticism over the Iraq war, the two men stuck together during the 2005 election campaign, at one point famously facing the cameras and eating ice cream. But the camaraderie sometimes seemed forced even though they rarely disagreed on the issues in public.
On one occasion as he sat beside Blair during that campaign, Brown was asked whether he would have done the same as the prime minister over Iraq. There was a long pause before Brown said, "Yes."
The government has declared its hopes to withdraw from front-line operations in Iraq this year, a move certain to please a public eager to see an end to involvement in the conflict. But in London, some expressed reluctance to believe it will be over soon.
"He'll find it difficult to divorce himself from the States," said Predrag Trsic.
As Blair finished his speech, he was mobbed, gripping hands and exchanging small talk with dozens of supporters - many wearing badges with his picture. Dozens carried homemade placards, one reading "Tony Rocks," another "Britain is better."
Some chanted "four more years," but were chided by Blair: "That's not on message for today."
"It was a very personal speech for Tony," said Hilary Armstrong, a former Cabinet minister. "I felt he was quite emotional, which is unusual for him - but this is an unusual day."
Blair left to greet members of his inner circle at his home in the election district, then headed back to London. Supporters were ushered from the party offices as staff hurriedly rearranged furniture for a wake in honor of local activist - whose funeral coincided with the leader's speech.
The 54-year-old Blair saved his long-expected announcement on his final day as prime minister for the district where he first won election to Parliament in 1983. The remarks came just days after he celebrated the 10th anniversary of Labour's landslide election victory of May 1, 1997, which ended an 18-year run in power by the Conservative Party.
Since then, he has been one of the most praised, and reviled, leaders in British history - the man who helped end Northern Ireland's "troubles" but angered many supporters by sending British troops to war in Iraq.
When he was elected at 43, Blair was the youngest prime minister of the 20th century, the first born after World War II and the only one to have played in a college rock band, Ugly Rumours. He transformed Labour from a social democratic party to a centrist "New Labour" and led it to three consecutive election victories - a first for the party.
Building on the market reforms of Conservative leader Margaret Thatcher, the stewardship of Blair and Brown has brought a thriving British economy. London rivals New York as the world's pre-eminent financial center, GDP is up, unemployment is down and interest rates are low, though rising.
However, Blair's promised reforms to health and education remain incomplete, and soaring house prices and increasing personal debt threaten to widen the divide between haves and have-nots.
Despite his accomplishments - not least an end to three decades of violence in Northern Ireland - Blair's legacy looks to be dominated by Iraq.
His decision to join Bush in committing troops to the invasion divided his party and the country. Blair said he was content for history to judge him, but four years on and with almost 150 British soldiers dead in Iraq, the war is more unpopular than ever.
His last months in office also have been overshadowed by a police investigation into claims his party and the opposition traded political honors for cash.
Senior Blair aide Ruth Turner, Blair's chief fund-raiser Lord Levy and one other wealthy donor have been arrested during the police inquiry into claims that seats in the House of Lords and other honors were awarded in exchange for party donations. Prosecutors are considering whether anyone should be charged.
Blair was questioned twice by police as a witness, although he is not considered a suspect. Turner attended Blair's speech Thursday.
In recent months, Blair's thoughts have turned to the lessons of his decade in power.
"When I first started in politics, I wanted to please everyone," he said during a tour of the Middle East in December. "After a time I learned that you can't please everyone, and you learn that the best thing is to do what you think is right and everyone can make their judgment."