Lib Dem leader Tim Farron says only his party can stop Theresa May winning the election.
Until today, May had repeatedly ruled out holding an early election, saying there would be no national vote until 2020.
The general election was due in 2020 but the Fixed Term Parliaments Act allows for this to be held earlier provided there is support from a minimum of two-thirds of MPs.
"That would be in nobody's interest", May said.
Preben Aamann, spokesman for Donald Tusk, president of the European Council of member states, said Brussels did not expect the timeline for the Brexit negotiations to be affected by an early general election.
The opposition Labour Party and Liberal Democrats welcomed the chance to put their policies to voters, though the Scottish National Party called the election a cynical political ploy.
Although the outcome of the vote was never in doubt, MPs used the debate to make party political points and to attack whichever party represents the greatest threat in their constituency.
Despite Corbyn's bravado, his party is demoralized and divided under his left-wing leadership and is expected to fare badly.
But Mr Corbyn dismissed her argument that she needs a fresh mandate to deliver Brexit, and said it was "extremely interesting" that she had chosen to call an election as the Crown Prosecution Service prepares to decide whether to press charges against a string of Tory MPs over allegations relating to 2015 general election expenses.
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The Sun, Britain's top-selling newspaper, splashed the headline "Blue Murder" - a reference to the Conservatives' party colour and the prospect of Labour losing dozens of seats.
May is hoping to gain a bigger majority in Parliament for her Conservatives. The government's current working majority is only 17 seats.
The Prime Minister said the only way to "guarantee certainty and stability for the years ahead" was to seek support from the public for her decisions.
The decision means that the election campaign can now begin in earnest.
Angus Robertson, leader of the SNP in Westminster, said May had changed her mind because she now realised the Brexit discussions were going to be much harder than Eurosceptics had imagined.
The spokesman noted that this did not mean there will be a delay in Brexit talks, "because negotiations were meant to start in June regardless of the United Kingdom government's decision to call an election on the 8th". The leaders of the 27 remaining European Union countries will meet on April 29 to agree the bloc's negotiating position, which will then be translated into a legal text by the European Union commission in May.
"It is unsustainable in the multimedia age of the 21st century to go to the country but not debate with the leaders of the other parties".
And Plaid Cymru leader Leanne Wood - whose profile received a major boost from her involvement in two of the 2015 broadcasts - said: "Theresa May should be empty chaired if she doesn't show up to any planned TV debates".