Sir Menzies Campbell has been elected leader of the Liberal Democrat Party.
Sir Menzies, 64, who was Lib Dem foreign affairs spokesman and acting leader, topped a ballot of party members after a five week campaign.
He beat economic affairs spokesman Chris Huhne in the final run off. Party President Simon Hughes came third.
Sir Menzies, who got 57% of the vote, said he was ready to take risks to "modernise" the party and lead it "back to government".
The new leader of the UK's third party, which won 22% of the vote in the 2005 General Election, said his election was a "victory for all Liberal Democrats".
Sir Menzies Campbell - 23,264
Chris Huhne - 16,691
Simon Hughes - 12,081
In his victory speech he pledged to fight for fairness, freedom and environmental protection.
But he added: "Let me make it clear now that caution and consolidation will not do.
"Safe pair of hands yes, but ready to take risks, ready to challenge orthodoxy and ready to challenge the party too."
He added: "Our task now is this: To build a strong, effective powerful Liberal Democrat party with the objective to ensuring a greener, fairer, decentralised and democratic Britain, a Britain at peace with itself at home and admired abroad."
Sir Menzies' age has been an issue during the campaign, but he told the BBC last week that he could see no reason why he could not be leader aged 72 - which would allow him to fight two general elections.
His first challenge as party leader will be to rally activists at the party's spring conference in Harrogate at the weekend.
Both defeated candidates pledged their support to Sir Menzies.
Mr Huhne said the new leader had a "hard-won and decisive mandate to lead this party to new advances with the backing of all of us".
He said the "thoughtful and good-tempered contest" had shown the party was the most united in Britain around the key issues.
"Collective wisdom is often so much greater than individual wisdom and Ming has undoubted authority, experience and credibility.
"I look forward to being a part of his team taking us to greater success," said Mr Huhne.
Mr Hughes, was eliminated in the first round of voting after coming third with 12,081, told his new leader: "I am absolutely clear that we will go, Ming, under your leadership from strength to strength towards the government that Britain desperately needs and that we are all so unitedly determined to achieve."
He too gave his "full support" for Sir Menzies. Asked on BBC News 24 if this was the end of his own leadership ambitions, he said: " "It is never the end of Simon Hughes".
He said he would carry on campaigning for a "more Liberal Britain
The voting system used for the election meant that after the first round, Mr Hughes' backers' second choices were transferred to Sir Menzies or Mr Huhne.
SNP leader Alex Salmond congratulated Sir Menzies on his success, saying he would "undoubtedly add gravitas to the Liberal Democrats".
But he added: "In electing Ming, the Lib Dems have broken one of the golden rules of politics which is that he who wields the sword should not inherit the crown.
"Ming was instrumental in the downfall of Charles Kennedy and that fact may come back to haunt his own tenure of leadership."
For Labour, Commons leader Geoff Hoon said the Lib Dems had to "reinvent themselves as a credible political party".
"For as long as they remain soft on crime and out of touch on issues like tackling anti-social behaviour, they cannot be taken seriously and will remain a protest group rather than a real party of government," said Mr Hoon.