Simon Hughes has become deputy leader of the Liberal Democrats.
The Bermondsey and Old Southwark MP last night saw off a direct challenge from his only rival, Tim Farron, sealing the votes of 38 of the party's 57 MPs.
After being chosen at a meeting of his fellow MPs, Hughes appeared alongside the Lib Dem leader and Deputy Prime Minister, Nick Clegg, on the steps of the House of Commons, where he promised the Lib Dems would "seize the moment" provided by the coalition government deal with the Conservative Party.
Thwarting any suggestion that he was not in favour of the coalition, Mr Hughes said: "Of course there are risks, of course there are challenges, and of course some party members and supporters were nervous, but bold decisions are always nervous.
"The alliance between the Liberals and SDP was a difficult decision to make. I supported it, it was the right decision. The coalition is the right decision."
Hughes, who ran unsuccessfully for the party leadership in 1999 and 2006, takes over from Vince Cable, who quit last month as deputy leader so that he could concentrate on his government job after becoming the Secretary of State for Business.
There has been speculation that Hughes, who did not take a job in the Conservative-Lib Dem coalition government, could become a figurehead for those in his party unhappy with the alliance.