The General Election will be held on May 5, Prime Minister Tony Blair announced today.
Mr Blair went to Buckingham Palace this morning to ask the Queen to dissolve Parliament.
Speaking afterwards in Downing Street he said: "I have just been to Buckingham Palace to ask the Queen to dissolve Parliament, which she has graciously consented to do.
"And there will be a General Election in Britain on May 5."
The Prime Minister said his "mission for the third term" was to entrench economic stability and public service investment, adding: "It's a big choice and there's a lot at stake".
He said the election was a big decision, adding: "The British people are the boss and they are the ones who will make it."
Downing Street said Parliament would be dissolved on Monday next week.
The new Parliament will meet on Wednesday May 11, when the first business will be the election of the Speaker and the swearing-in of members.
The State Opening will be on Tuesday May 17.
Mr Blair said the election campaign gave him the chance to go out to the country and restate the one thing that motivated him personally.
He said he wanted to create a country where whatever people's background, they had the chance to make the most of themselves.
Speaking about the choice facing the country he said: "It is a big choice, a big decision.
"The British people are the boss and they are the ones that will make it."
The announcement confirms Westminster's worst-kept secret and brings to an end the "phoney war" of the pre-election campaign which has already been waged for weeks.
Mr Blair had been expected to name the day yesterday, but the announcement was put off because of the death of the Pope.
The Conservatives and the Liberal Democrats launched their campaigns this morning before the official announcement.
Speaking in London, Tory leader Michael Howard said voters faced a clear choice.
"They can either reward Mr Blair for eight years of broken promises and vote for another five years of talk," he said.
"Or they can vote Conservative, to support a party that's taken a stand and is committed to action on the issues that matter to hard-working Britons."
And Liberal Democrat leader Charles Kennedy promised a positive campaign.
Speaking in Newcastle, he said his party would be "positive and ambitious" for Britain.
"I am not going to spend these next few weeks going around talking Britain down," he said.
"I am going to be addressing people's hopes, not playing on people's fears."
The election will take place on the same day as local elections across much of England and Northern Ireland.
Labour goes into the campaign with a narrow lead, according to a number of opinion polls published today.
However, a Mori poll for the Financial Times puts the Conservatives five points ahead of Labour among people who say they will certainly vote.