Hague announced his resignation in a Twitter message that read: "Tonight I am standing down as Foreign Secretary after four year to serve as leader of the House of Commons."
Tonight I am standing down as Foreign Secretary after 4 years to serve as Leader of the House of Commons— William Hague (@WilliamJHague) July 14, 2014
British Prime Minister David Cameron responded via Twitter, writing "I'd like to pay an enormous tribute to William Hague who is standing down as an MP at the next election. Until then, I'm delighted he'll remain my de facto political deputy, play a key campaigning role and be Leader of the House of Commons."
Hague's resignation is the latest in a series of Cabinet reshuffles ahead of the general election, although it came as a surprise for Westminster, which expected Hague to stay on through the election.
"In government there is a balance to strike between experience on the one hand and the need for renewal on the other," Hague explained on Monday, "and I informed the prime minister last summer that I would not be a candidate at the next general election."
"Accordingly I am stepping aside as foreign secretary, in order to focus all my efforts on supporting the government in parliament and gaining a Conservative victory in the general election -- after four years in which we have transformed Britain's links with emerging economies, significantly expanded our diplomatic network and the promotion of British exports, restored the Foreign Office as a strong institution, and set a course to a reformed European Union and a referendum on our membership of it."
Hague was appointed foreign minister in 2010. It is expected that the prime minister will announce Defense Secretary Philip Hammond as Hague's successor.