David Cameron has entered 10 Downing Street as Prime Minister promising to lead Britain through to "better times ahead".
Arriving from his audience at Buckingham Palace where he formally "kissed hands" with the Queen, the Conservative leader said he intended to form a "full and proper" coalition with the Liberal Democrats.
With his wife Samantha by his side, he declared: "This is going to be tough and difficult work. Coalition will throw up all sorts of difficulties but I believe that together we can provide that strong and stable government that our country needs."
His arrival was marked by a telephone call from President Barack Obama in the White House congratulating him on his appointment.
Less than two hours earlier, Gordon Brown had emerged to announce that he was making his own journey to the Palace to tender his resignation, bringing down the curtain on 13 years of Labour government.
Liberal Democrat leader Nick Clegg will be the Deputy Prime Minister, sitting as one of five Lib Dem ministers in the new Cabinet.
The announcement came shortly before a deal to form a coalition government with the Conservatives was approved by Liberal Democrat MPs, peers and the party's ruling federal executive.
Mr Cameron's close ally George Osborne will be the new Chancellor of the Exchequer while William Hague is Foreign Secretary. It was reported that Andrew Lansley would go to the Department of Health, keeping his shadow cabinet portfolio.
Mr Cameron said he and the Lib Dem leader were both prepared to put aside their party differences and "work hard for the common good and for the national interest". "I believe that is the best way to get the strong Government that we need, the decisive Government that we need today," he said.
"I think the service our country needs right now is to face up to our really big challenges, to confront our problems, to take difficult decisions, to lead people through these difficult decisions so that together we can reach better times ahead."
The agreement between the two parties, reached five days after an inconclusive election, ends 13 years of rule by the Labour Party under Tony Blair and his successor Gordon Brown.
The untested partnership will have to clean up public finances, with a record budget deficit running at more than 11 percent of national output.
Markets welcomed the agreement, hopeful that a government led by the centre-right Conservatives will take swift action to bring down spending.
"This is going to be hard and difficult work. A coalition will throw up all sorts of challenges. But I believe together we can provide that strong and stable government that our country needs," Cameron said in his first speech as prime minister.
The Liberal Democrats were also celebrating after decades spent in the shadow of Labour and the Conservatives.
"There will of course be problems, there will of course be glitches. But I will always do my best to prove new politics isn't just possible, it is also better," Liberal Democrat leader Nick Clegg, who will be deputy prime minister, told reporters.
His party put its final seal of approval on the deal at a meeting that ended after midnight on Tuesday.
Cameron, a 43-year-old former public relations executive, took over as prime minister just hours earlier when Brown admitted defeat in his own efforts to broker a deal with the Liberal Democrats.
He is Britain's youngest prime minister in almost 200 years.
The Liberal Democrats have more in common with Labour in policy terms, but talks to form what the media called a "coalition of losers" swiftly fell apart.
The Conservatives are the largest party in parliament after last week's election but fell 20 seats short of an outright majority. Combined with the Liberal Democrats, they will have a majority of 76 seats.
OSBORNE TO BE FINANCE CHIEF
The prime minister's office announced late on Tuesday there would be five Liberal Democrats in cabinet in total, including Clegg.
It did not name the other four ministers but there were reports Vince Cable, the highly regarded Liberal Democrat Treasury spokesman, would be given a role overseeing banking and business.
A Conservative source said the two parties had agreed to significantly accelerate deficit reduction plans. The focus would be more on cutting public spending than on raising taxes.
Another Conservative source said George Osborne, a close friend and ally of Cameron, would become the new Chancellor of the Exchequer (finance minister).
Some in the finance industry have expressed doubts about Osborne because he is untested and takes over an economy emerging from the worst recession since World War Two.
William Hague, a former Conservative leader and one of the main negotiators with the Liberal Democrats, will be the foreign minister.
(Additional reporting by Michael Holden and Adrian Croft)
-Yahoo UK News.