MPs are expected to give their approval to Theresa May's plan for a snap election on June 8, in a Commons vote the day after her shock announcement.
Under the terms of the Fixed-Term Parliaments Act, Mrs May must secure a two-thirds majority of MPs to bring the election forward by three years from the scheduled date of May 2020.
She told The Sun she decided to reverse earlier pledges not to go to the country early because she wanted to be able to go into Brexit negotiations with the "backing of the British people" as her "very clear mandate".
Both Labour and Liberal Democrats have officially welcomed the early poll and are expected to back it in Wednesday afternoon's vote.
Labour leader Jeremy Corbyn faced down calls from some MPs at a Westminster meeting on Tuesday evening for the party to abstain in the hope of forcing Mrs May to call a vote of no confidence in her own government.
Aides were unclear whether he will impose a three-line whip on MPs to vote in favour.
Mrs May said she was concerned that opposition parties would seek to derail Brexit by voting against key pieces of legislation including the Great Repeal Bill, which will provide the legislative authority to take Britain out of the European Union.
Having repeatedly ruled out calling a snap election in the past, Mrs May said she had "reluctantly" taken the decision to go to the country after seeing other parties "playing games" with the process of preparing for Brexit negotiations.
Her final decision was taken during a walking holiday in Snowdonia with her husband Philip and she told the Queen on Easter Monday before getting the full approval of Cabinet on Tuesday morning.
Speaking to The Sun, Mrs May said: "What I hope comes out of the election is support from the public to say we agree with their plan for Brexit, so that when I go into Europe I've got that backing of the British people".
She also revealed a concern that the May 2020 election date stipulated by the Fixed-Term Parliaments Act would leave her vulnerable to pressure from Brussels as she neared the end of the two-year withdrawal negotiations in March 2019.
"If we're negotiating at a point that is quite close to a general election, I think the Europeans might have seen that as a time of weakness when they could push us," she explained. "Now we will be much freer."
The gap before talks begin in earnest in June gave her a "window of opportunity" to strengthen her hand by improving her slim 17-seat majority and pushing the next election date back to 2022, by which time the UK should have long ago left the EU.
Mrs May indicated that Conservative candidates will be expected to sign up to her election manifesto in full, putting pressure on remaining Europhiles within her party to toe the line.
She insisted that the election would not focus solely on EU withdrawal but would see Conservatives set out plans for "the UK beyond Brexit".
And she set out her line of attack against Labour, saying voters would face a choice between "stable and strong leadership, which I hope they have seen, and a coalition of Corbyn supported by the Liberal Democrats and the SNP".
Mr Corbyn said Mrs May's decision had given voters the chance "to vote for a government that will put the interests of the majority first", while Liberal Democrat leader Tim Farron said the election provided an opportunity to block "a disastrous hard Brexit".
Scottish First Minister Nicola Sturgeon described the election call as "a huge political miscalculation by the Prime Minister" which would allow the SNP to reinforce its democratic mandate to stage a second referendum on independence.