The House of Commons on Wednesday will vote whether to approve the early election.
Tim Farron, leader of the Liberal Democrats, who have campaigned for a referendum to be held on the terms of Brexit, said the election proved a chance to change the country's direction.
Working off her predecessor David Cameron's slimly won majority, May had been reluctant to call for an election when Cameron stepped down in June after the unexpected results of the European Union referendum threw the country, and the Conservative Party, into turmoil. "What we need to do is to be very careful about what we're going to do after Brexit".
The other 27 European Union leaders are set to hold a summit on April 29 where they will agree on a strategy for negotiating Britain's expected departure in 2019.
Jeremy Corbyn (Islington North), the Labour leader, has already said he welcomes it.
Beyond Brexit, May can also now respond to those who claim her domestic policy agenda (think grammar schools) lacks a mandate.
Q Why did Mrs May change her mind?
Does this mean the next general election will be in 2022?
May wants a fresh mandate for her Brexit negotiations and believes that a newly elected, majority Tory government will make it harder for her political opponents (at home and abroad) to chip away at her authority during the Brexit negotiations.
"The Liberal Democrats have said they want to grind the business of government to a standsill".
"They underestimate 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". The UK adopted new laws in 2011 that greatly reduced the authority of the prime minister to call new elections outside of the regularly scheduled five-year cycle; it now takes two-thirds of Parliament to approve such a call.
In contrast a shock win (highly unlikely) for the Labour Party, would place the future of Brexit in question.
After months of assertions that she would not call an election, Ms May threw the gauntlet down to other party leaders to back her proposal.
Kallum Pickering, senior economist at Berenberg, said a big win for May in the June election would make a hard Brexit more likely.
Rather than helping the country unite, the election could widen divisions within the United Kingdom.
Scotland's First Minister Nicola Sturgeon accused May of using the early election as an opportunity to impose deeper cuts.
However others are sure that this strategic move from May will ensure her success in the election so that she can become Prime Minister with voter backing.
The Scottish National Party now holds 54 of Scotland's 59 seats in the British Parliament, making it the third-largest party there.