William Hague has resigned as British Foreign Secretary and will leave the House of Commons next year.
His decision comes as British Prime Minister David Cameron reshuffled his cabinet and wielded the axe to clear the way for a new generation.
Former Conservative Party leader Mr Hague will replace Andrew Lansley as Leader of the Commons.
He will lead the Conservative Party campaign in key constituencies, particularly in northern England, until he gives up his safe seat in Richmond, North Yorkshire.
"Tonight I am standing down as Foreign Secretary after four years to serve as Leader of the House of Commons," Mr Hague wrote on Twitter.
"I will not stand as an MP in the May 2015 General Election."
Mr Cameron said Mr Hague had been one of the Conservative Party's "leading lights" for a generation and had been a "close confidante, wise counsellor and great friend".
Defence Secretary Philip Hammond is favourite to replace Mr Hague.
The shock announcement follows the widely expected decision by Ken Clarke to retire at 74, ending a career in government stretching back to 1972.
Renewal in politics is good, and holding office is not an end in itself. After 26 years as an MP time will be right for me to move on— William Hague (@WilliamJHague) July 14, 2014
In a reshuffle that has been much wider than expected, David Jones was sacked as Welsh secretary, Dominic Grieve was reported to have lost his job as attorney general and Owen Paterson was rumoured to be heading to the exit as environment secretary despite a rearguard effort by allies to keep him in office.
Universities minister David Willetts stood down and declared his intention to quit as an MP next year, while Nick Hurd said he was leaving his post as minister for civil society.
Greg Barker, who helped run Mr Cameron's Tory leadership bid, quit as energy and climate change minister and will give up his seat next year.