Ken Livingstone will face Boris Johnson in the 2012 election to be London mayor after overwhelmingly winning the Labour party candidacy.
The result means Mr Livingstone, at the age of 67, will run for the fourth time as a mayoral candidate.
He will face the current Conservative mayor Boris Johnson in a re-run of the 2008 election.
Mr Livingstone thanked his supporters and said he would defeat what he described as “the current disastrous administration in City Hall”.
He pledged to campaign on an anti-government ticket.
“We will unite Londoners around a message to [David] Cameron and [George] Osborne that we don’t want these cuts. If you want to get them out, you start by getting out Boris Johnson,” he said.
Labour history
Ken Livingstone is a veteran political campaigner with a near 40-year history in London politics.
In 1971, when he was elected to Lambeth Borough Council.
We will unite Londoners around a message to Cameron and Osborne that we don’t want these cuts. Ken Livingstone
He led the Greater London Council (GLC) from 1981, where he was dubbed “Red Ken” for his left-wing politics.
In 1986, the council was scrapped by Prime Minister Margaret Thatcher.
Mr Livingstone was elected MP for Brent East from 1987 to 2000, however was expelled from Labour for a period after standing as an independent in the first mayoral election.
During his eight years as London mayor, Mr Livingstone introduced the congestion charge and the Oyster card.
He had stood as an independent in 2000, and was picked as Labour candidate in 2004 and 2008.
Victory in May 2012 would mean Mr Livingstone being mayor during the 2012 Olympics and Paralympics, events which he been prominent in the campaign to secure.
However an opinion poll this week suggested that Mr Johnson is likely to be re-elected.