Theresa May today called on MPs to agree to a snap General Election to be held on June 8.
The Prime Minister used to a statement in Downing Street to set out the case for going back on her previous pledge there would be no election ahead of 2020.
Mrs May said the lack of "unity" in Westminster over the Brexit process was weakening the Government's negotiating hand with Brussels and meant an election was required.
Explaining the timing, Mrs May said it would coincide with the European Union leaders finalising their Brexit negotiating position and come before full talks begin.
Without a snap general election, Mrs May said "political game-playing" in Westminster would continue and lead to negotiations with the EU reaching their "most difficult stage" in the run-up to the previously scheduled 2020 vote.
"Division in Westminster will risk our ability to make a success of Brexit, and it will cause damaging uncertainty and instability to the country," she said.
"So we need a general election and we need one now.
"Because we have at this moment a one-off chance to get this done, while the European Union agrees its negotiating position and before the detailed talks begin."
Under the terms of the Fixed Term Parliament Act, MPs will have to vote for an early election in Parliament tomorrow.
Mrs May has repeatedly rejected the case for an early election and admitted in Downing Street she had only recently changed her mind.
"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."