Here’s the rundown.
British governments generally last for five years, and the Conservative Party’s administration — then led by May’s predecessor David Cameron — was elected in 2015. The next election was not due to take place until May 2020.
Why is it happening?
May, who took over when Cameron resigned in the wake of Britain’s decision to leave the European Union, wants to seek a stronger mandate in Brexit talks.
But her party only has a slim majority in Parliament, and opposition parties have attempted to throw rocks in her path towards Brexit.
She also faces divisions in her own party over Brexit tactics — although perhaps not surprisingly, May didn’t mention those on Tuesday.
“There should be unity here in Westminster, but instead there is division. The country is coming together, but Westminster is not,” she said. “We need a general election and we need one now.”
Why is this such a shock?
“I’m not going to be calling a snap election,” May told BBC journalist Andrew Marr in September 2016. “I’ve been very clear that I think we need that period of time, that stability, to be able to deal with the issues that the country is facing and have that election in 2020.”
Only a month ago, her spokesman firmly ruled out an early vote. “There is not going to be a general election,” he said on March 20.
May said she had changed her mind on a recent walking holiday with her husband in Wales.
What happens now?
Opposition parties said they would not block her plans, which means that Britain will go to the polls on June 8.
Could she lose the election?
According to a recent string of polls, the Conservatives are heading for a sweeping victory.
What could it mean for Brexit?
If May wins, it will shore up May’s strategy for Brexit. In voting for the Conservative party, the British people will be giving May a mandate to carry out Brexit the way she sees fit.
The main opposition Labour Party has also committed to carrying out the desire of Britons to leave the EU, expressed in last year’s referendum. Only the Liberal Democrats, a minority party, opposes Brexit.
In any case, the UK is already bound by Article 50 of the Lisbon Treaty, which May triggered last month. By invoking Article 50, the British government has set the process of withdrawing from the European Union in motion.
Legal experts are divided on whether it can be revoked — but there’s no chance of that being attempted anyway.
As May said in Downing Street: “Britain is leaving the European Union and there can be no turning back.”