The snap general election called by Theresa May on June 8 "will help Brexit negotiations".
The Prime Minister said divisions at Westminster risked hampering Article 50 negotiations with the European Union, and said she wanted “unity” as talks begin in earnest.
The announcement came as a surprise, with Mrs May and Downing Street previously saying the country would not go to the polls before 2020.
Labour leader Jeremy Corbyn said his party would put the interests of the majority first.
General Election 2017
Speaking on the steps of Downing Street, Mrs May, who works with a working majority of just 17 MPs, said: “We want a deep and special partnership between a strong and successful European Union and a United Kingdom that is free to chart its own way in the world.
“That means we will regain control of our own money, our own laws and our own borders and we will be free to strike trade deals with old friends and new partners all around the world.
“This is the right approach, and it is in the national interest. But the other political parties oppose it.
“At this moment of enormous national significance there should be unity here in Westminster, but instead there is division. The country is coming together, but Westminster is not.”
She acknowledged that she needed a stronger position in the Commons to secure her plans for the UK’s future outside the EU.
“Our opponents believe because the Government’s majority is so small that our resolve will weaken and that they can force us to change. They are wrong,” she said.
“They under-estimate our determination to get the job done and I am not prepared to let them endanger the security of millions of working people across the country, because what they are doing jeopardises the work we must do to prepare for Brexit at home and it weakens the Government’s negotiating position in Europe.”
Under the Fixed-Term Parliaments Act, general elections take place every five years, meaning Mrs May would have had to carry on until 2020 before the chance to strengthen her position.
In order to call the early election, she will need the support of two-thirds of the 650 MPs in the Commons - but Labour is expected to support her, as any opposition would look weak if it did not agree to the chance to take office.
Senior Tories have urged Mrs May to call an early election, taking advantage of the Conservatives’ healthy opinion poll lead over Jeremy Corbyn’s Labour.
Mrs May suggested she reached her decision over the Easter parliamentary recess - during which she went on a walking holiday in North Wales.
“I have only recently and reluctantly come to this conclusion,” the PM said.
“Since I became Prime Minister I have said that there should be no election until 2020.
“But now I have concluded that the only way to guarantee certainty and stability for the years ahead is to hold this election and seek your support for the decisions I must take.”
Mr Corbyn said he looked forward to the election fight: “I welcome the Prime Minister’s decision to give the British people the chance to vote for a government that will put the interests of the majority first.
“Labour will be offering the country an effective alternative to a government that has failed to rebuild the economy, delivered falling living standards and damaging cuts to our schools and NHS.
“In the last couple of weeks, Labour has set out policies that offer a clear and credible choice for the country. We look forward to showing how Labour will stand up for the people of Britain.”
In the 2015 elections, Conservatives retained all 11 seats in Surrey .
