Former senior police officer Brian Paddick will run for Mayor of London in May 2008 as the Liberal Democrat candidate.
The 49-year-old won 73% of the first preference votes in a ballot of London party members.
He promised “less crime, better transport, cleaner air and fewer Londoners living in poverty are all crucial in making sure that London remains one of the most exciting cities in the world.”
He faces incumbent Ken Livingstone and Tory candidate Boris Johnson in next May’s election.
Mr Paddick was the UK’s most senior out gay policeman until his retirement as Deputy Assistant Commissioner of the Metropolitan Police in May this year.
He told the BBC that he thinks he can win despite his low profile compared to the main party candidates and claimed he is the only serious alternative to Mayor Livingstone, whom he called “a nice guy.”
“There are a number of things that Ken has done reasonably well,” he said.
“But putting up the mayoral precept of the council tax by 100% in four years sounds a bit extravagant.
“There’s a lot of waste and I think I can do better, so what I’m offering people is ‘Ken-plus’ if you like – not getting rid of everything Ken has done and starting again.”
In September he admitted to the Evening Standard that he had a meeting with the Conservative party about being their candidate for Mayor of London before deciding to seek the Lib Dem nomination.
Mr Paddick came to public prominence as borough commander of Lambeth, when his policy of targeting resources at class A drug dealers and taking a more relaxed approach to cannabis use caused right-wing outrage.
The policy was popular with locals, and his direct style of policing helped to foster a trust and respect with many who viewed the police with suspicion.
He has been critical of the decision of Prime Minister Gordon Brown to raise the classification of cannabis to a Class B substance, but said he thinks the drug is harmful.
Mr Paddick called for a public enquiry into the terrorist attacks on London on July 7th 2005, something the government insists is unnecessary.
The election for Mayor of London will be held on May 1st 2008. Mr Livingstone is seeking a third four-year term of office.