Ken Livingstone will mount a bid to return as London's mayor in 2012, he has confirmed.
He said he would "love" to return to the role he held for eight years, having been replaced as mayor by Boris Johnson in May last year.
Mr Livingstone said he would run as an Independent nominee if he was not selected as a Labour candidate.
However, he said he would be too old to try to replace Gordon Brown as Prime Minister.
The 63-year-old former MP for Brent East told Total Politics magazine that he was "as certain as you can be, two-and-a-half years ahead" that he would run for re-election as mayor.
Conservative candidate Mr Johnson beat him by 139,772 votes in last year's mayoral election.
Mr Livingstone said he was attending Mayor's Question Time at the London Assembly in order to prepare himself for the campaign to come.
He said he wanted to be chosen as the Labour candidate again and said he wanted to know more about Mr Johnson's campaign "than he does".
Mr Livingstone ran as an Independent candidate in the first mayoral election in 2000 after claiming Labour altered its selection rules to ensure Frank Dobson was picked as the party's official candidate instead of him.
He predicted the party would once again seek to block his nomination.
On Thursday a Labour Party spokesman said: "The process of finding a candidate is a long way off and would be a decision for party members."