Ed Davey has replaced Chris Huhne as Energy Secretary, Downing Street announced today.
Norman Lamb, parliamentary aide to Nick Clegg, has been promoted to Mr Davey's old post as business minister and Cardiff Central MP Jenny Willott becomes assistant whip.
Ed Davey's promotion to the Cabinet marks the high point of a career in politics which began just six months after he graduated from university.
The Liberal Democrat MP for Kingston and Surbiton has won plaudits for handling the thorny issue of Royal Mail privatisation as a minister in Vince Cable's Business Department since the coalition Government came to power.
But his involvement with the party stretches back to 1989, when he found a job as an economic researcher shortly after graduating from Oxford.
Born on Christmas Day 1965, the 46-year-old served in a variety of influential roles for the Liberal Democrats after his election as an MP in 1997.
He was chief of staff to former leader Sir Menzies Campbell and was appointed as the party's foreign affairs spokesman by Nick Clegg.
During his time on the Lib Dem frontbench he was thrown out of the Commons for a day in 2008 after clashing with deputy speaker Sir Michael Lord in a row over Europe.
His popularity and standing within the party as a member of the modernising "Orange Book" wing meant he was earmarked for ministerial office once the coalition was formed.
Between his first stint working for the Lib Dems and his election in 1997, Mr Davey worked as a management consultant, specialising in postal companies and this background meant he was ideally placed to take through the coalition's privatisation plans for the Royal Mail.
As Postal Affairs Minister he argued the case for selling off the Royal Mail, facing fierce opposition from the Communication Workers Union.
He was also heavily involved in tackling business red tape and considering reviewing employment regulations.
Mr Davey, who was orphaned at 15, attended Nottingham High School and graduated from Jesus College, Oxford with a first in politics, philosophy and economics.
A fan of Notts County, Mr Davey's interests include walking, films, music, squash and swimming.
In 1994 he received awards from the Royal Humane Society and the chief constable of the British Transport Police for rescuing a woman from the path of an oncoming train at Clapham Junction in south London.
The Liberal Democrats will hope he will rescue the party's reputation in Government, which has been tarnished by the resignation from the Cabinet of Chris Huhne.