Dame Tessa Jowell has fuelled speculation she is preparing for a bid to run as London's mayor as she announced she will retire as an MP at the next general election.
The Labour stalwart, who as culture secretary played a central role in bringing the 2012 Olympics to London, announced she was ending her Commons career after 23 years in 2015.
In a letter to her Dulwich and West Norwood constituency party she said quitting the south London seat was "the hardest decision I have ever taken".
Her announcement drew tributes from Tony Blair and Lord Coe who said she had been an "inseparable part" of the success of the Games.
But she left the door wide open to seeking a still more prominent role in the capital when Boris Johnson's current term in City Hall ends in 2016.
"It is really too early for anyone to be declaring themselves ahead of the local elections next year and the general election in 2015," she said.
"I love London and, of course, when the time comes will think hard about whether I should offer myself as a candidate."
Mr Blair, whose initial reluctance to bid for the 2012 games was overcome by Dame Tessa, said that as well as being an able and determined politician, she was "kind, decent and loyal in a way I have seldom seen in politics".
British Olympic Association chairman Sebastian Coe said she was the "political driving force" behind the 2012 bid and "an inseparable part of their ultimate success".
And Labour leader Ed Miliband, who kept her on as shadow Olympics minister after becoming leader in 2010, said that while the Olympics would be her "greatest legacy", she was a " unique politician" of warmth, spirit, loyalty and generosity.
In her letter explaining the decision, Dame Tessa, 66, said it had been an " extraordinary privilege" to serve in government throughout the whole of Labour's three terms in office from 1997.
"I know that you share with me a belief in the extraordinary responsibility of representation, the power of politics, the decency of politics and its capacity to make known, and put to use, the best of human nature," she told local activists.
"We also accept that the job is never done, but I feel that the time is now right, for the constituency definitely and for me probably, to give somebody else the chance to take the next steps forward."
An ardent Blairite who backed David Miliband for the party leadership in 2010, she said his brother would be a "great prime minister".
The Opposition leader told her in a letter: "Your willingness to think creatively and your perseverance played a key role in improving the lives of millions of children by introducing affordable childcare and Sure Start. And you can be rightly proud of your role in the New Deal to get the long-term unemployed into jobs.
"However, your greatest legacy is bringing the Olympics to Britain. Every great moment in a nation's cultural or sporting life needs people who see the possibilities and dare to dream. That was you."
Mr Blair said: 'Tessa Jowell is a very unusual type in the often brutal world of politics.
"She is immensely able, tough-minded and determined. But at the same time and with the same people, she is kind, decent and loyal in a way I have seldom seen in politics.
"I always knew I could rely on her and trust her 100%. But I also knew she would never hesitate to tell me what she thought was right and true. That gave and gives her a rare integrity.
"She represents all that is best in Labour and is a great advocate for Britain. I have no doubt that she will continue to do great things in the service of both."
Appointed a health minister in Mr Blair's first government line-up, Dame Tessa then moved to education before succeeding Chris Smith as culture secretary after the 2001 general election - going on to introduce the BBC Trust.
While she lost the Cabinet role when Gordon Brown took over, she retained responsibility for the Olympics and the capital and continued to attend Cabinet - finding herself back at the top table as Cabinet Office minister in the 2009 reshuffle.
Tottenham MP David Lammy - another of those who have expressed an interest in being Labour's London mayoral candidate - was among those paying tribute on Twitter.
"Sad my good friend standing down," he wrote.
Shadow business secretary Chuka Umunna paid tribute to his " Lambeth neighbour, political mum and Labour legend".