The snap election caps a tumultuous few years in British politics that has seen two historic referendums and a prime ministerial resignation.
May, who made the shock call for an early election on Tuesday, needs to bolster her narrow majority of 17 seats ahead of likely tortuous talks with Brussels that could re-open old wounds within her Conservative Party.
"I believe this will strengthen our hand in negotiations," May told BBC Radio 4's Today programme on Wednesday, arguing that opposition parties were "intent on frustrating the Brexit process".
May had for months ruled out an early election, but switched tack saying it was needed for "certainty and stability" ahead of the Brexit negotiations.
The small Liberal Democrats opposition party is hoping to emerge as a haven for pro-European voters distraught after last June's referendum to quit the European Union, gearing up to campaign against a "hard Brexit" that would take Britain out of Europe's single market.
But experts say the main opposition Labour Party is in a weaker position ahead of the proposed June 8 election, bitterly divided over both its leftist leader Jeremy Corbyn and how to respond to Brexit.
Opinion polls put the Conservatives -- who currently hold 330 of parliament's 650 seats -- well ahead of Labour, who have 229.
Three polls released over the weekend show May's Conservatives about 20 points ahead.
May, Britain's second female prime minister, who took over last summer following her predecessor David Cameron's failure to convince voters to back the EU, also appears to have won strong popular support for her handling of the political earthquake unleashed by Brexit.
"May heads for election landslide," read The Times' front page on Wednesday.
The Telegraph reflected the nation's surprise at the imminent election: "May's bolt from the blue".
For Michael Hewson, an analyst at CMC Markets, the elections could also help May by "diluting the influence of the more extreme elements of her own party on the Brexit process".
Labour's embattled Corbyn, meanwhile, faces speculation that a dismal performance in the election would spell the end of his time at the helm of the fractured 117-year-old party.
So far, Labour's stance has been to allow the government to go ahead with the EU divorce -- but only under certain conditions, such as retaining strong economic ties with the bloc.
That approach has left neither of the party's key constituencies particularly happy.
"Core voters in the north who voted for Brexit are not convinced, and metropolitan liberal voters aren't convinced by that either," political expert and author Eliza Filby told AFP.
Many of Labour's traditional working-class supporters voted to leave the EU, particularly in areas that have experienced a large influx of eastern European immigrants in recent years.
The announcement caught British political observers off guard as well as financial markets, which retreated as investors reacted cautiously to May's speech.
Britain's next election had been scheduled for May 2020, but a two-thirds majority in parliament could overrule that in Wednesday's vote, which British media reported could come at around 1300 GMT after an hour and a half of debate.
Labour has already said it supports an early election.
Scottish First Minister Nicola Sturgeon, who is pressing for an independence referendum, said May was making a "huge political miscalculation" that would bolster her Scottish National Party.
Scotland voted overwhelmingly to remain in the EU and Sturgeon argues it should now be allowed to break off from Britain to hold on to close ties with the bloc.
If the election goes ahead, parliament would be dissolved from May 3 and the campaign would begin in earnest, just days after EU leaders hold a special summit to agree a negotiating strategy for Brexit on April 29.
The Brexit negotiations are expected to start in June.
The snap election caps a tumultuous few years in British politics that has seen two historic referendums -- one on Brexit, another on Scottish independence -- and a prime ministerial resignation.
An early election would therefore be the fourth big vote in four years starting with the general election of 2015.