Nick Clegg is the new leader of the Liberal Democrats.
He won a narrow victory of just 511 over the party’s environment spokesman Chris Huhne.
Mr Clegg won 20,988 votes to Mr Huhne’s 20,477. An estimated 65,000 ballot papers were sent to Lib Dem members.
At 40, he is the youngest party leader in the Commons and 26 years younger than his predecessor Sir Ming Campbell.
The result of the election was announced this afternoon to a large audience in a central London hotel by acting Lib Dem leader Vince Cable.
Former party leaders Paddy Ashdown, Charles Kennedy, Ming Campbell and David Steel were all present to see the result.
“Today is about two things – ambition and change,” Mr Clegg said in his acceptance speech.
“Renewed ambition for the Lib Dems, renewed ambition to reach out to the millions of people who I know share our instincts and values but do not yet vote for us.
“Renewed ambition for Britain we want to change politics and change Britain.”
He thanked his opponent for his “energetic” campaign.
“As of now, we are colleagues once again and I look forward to working closely with you,” he said.
He thanked Vince Cable for the “spellbinding” way that he has led the party in the last two months, and paid tribute to Ming Campbell, saying that without him: “I just don’t think this party would have the great future we now know lies ahead of us.”
Mr Clegg has been an MP since 2005 and so could not have voted for most LGBT equality legislation.
He voted in favour of outlawing discrimination on the grounds of gender reassignment but was absent from votes on the Sexual Orientation Regulations.
Sir Menzies Campbell stood down as leader in October, having led the party since March 2006, when long-serving leader and fellow Scot Charles Kennedy resigned over press reports of about alcoholism.
His decision to stand down was influenced by the Prime Minister’s announcement that he would not be calling a general election until 2009 and by persistent media attention on his age.
Last month, in an exclusive interview with PinkNews.co.uk Mr Clegg said that he is “absolutely in favour” of a proposed new law to make incitement to hatred on the grounds of sexual orientation an offence.
He dismissed concerns from some gay commentators that the law is unnecessary, saying there is a “real problem of overt homophobic incitement to violence.”
The party’s 2005 manifesto promised legislation to tackle this issue.
“I passionately believe that there is a real problem,” Mr Clegg said.
“I have become persuaded by the evidence put forward by Stonewall that this is a real issue.
“What we did on the religious hatred bill shows that we can strike the right balance between making sure that hateful crime does not take place but at the same time protecting peoples right to free speech.
“Under my leadership I will make absolutely sure that we are at the forefront of getting the balance right with this legislation.”
Mr Huhne paid tribute to his new leader’s ability to reach out to young people, and said the party would see “even greater success in the future.”