For the first time since coming to office in 1997, Mr Blair let it be known that he intends to serve a full, five-year second term if returned to power.
He will then lead New Labour into a third election and could challenge Baroness Thatcher's record 11 years at Number 10.
The move knocks on the head Westminster speculation that he would stand down mid-way through a second term, and sounds the death knell for Gordon Brown's dreams of becoming party leader.
The Chancellor, who will be in his late 50s if Mr Blair wins his decade in power, looks doomed to become the Prince Charles of politics.
Most Labour MPs now accept that having beaten him in Labour's leadership contest after the death of John Smith, Mr Blair has consigned Mr Brown to be "always the bridesmaid".
The Prime Minister's official spokesman ended speculation about Mr Blair's future plans ahead of the party's centenary conference in Bournemouth this week. He said: "The Prime Minister certainly doesn't take a second term for granted ... he remains eternally vigilant against complacency."
But asked if Mr Blair would ask voters to trust him for a full, second term and back the Labour party with him in charge of it, the spokesman replied: "He certainly will. Yes."
Mr Blair, whose personal poll rating leaves all rivals in the shade, intends to heap praise on Mr Brown in his platform speech to conference on Tuesday. "It is widely acknowledged, rightly, and supported by indicators that Gordon has done a brilliant job and the tough decisions early on have paid off," Mr Blair's spokesman said.
Both have pledged to make Labour the party of "economic competence". A tough line on spending will be the main thrust of their conference message.
Sources close to Mr Brown were last night stressing the united front between Chancellor and Prime Minister. One said: "As far as Gordon is concerned, Tony is going to stay on forever, or at least until he decides not to go on anymore.
"There was never a deal between them that Tony would step down to give Gordon a go. The only deal was that he would be Chancellor."