Prime Minister Theresa May of Britain is calling for a snap election on June 8, breaking a promise not to seek a vote before 2020. Here are answers to some questions about the election and Mrs. May’s decision.

The British do not vote directly for their prime minister. Instead, they vote for a candidate to represent their district in Parliament. The leader of the party that wins the most seats in Parliament normally becomes the prime minister. Historically, prime ministers could call an election whenever they chose. But in 2011, Parliament passed a law that scheduled a general election every five years — with two exceptions. If the members of Parliament lose confidence in the government, or if two-thirds of the members agree, a “snap” election can be held. Mrs. May, the current prime minister and leader of the Conservative Party, believes she has the votes to hold an early election.

Mrs. May took office less than a year ago, when her predecessor, David Cameron, resigned after losing the June 23 referendum on British membership in the European Union, known as Brexit. At the time, she promised to carry out voters’ wish to leave the union. She also said she would not seek an early election.

However, Mrs. May has since staked her legacy on Brexit. With only a small working majority in Parliament at the start of what is expected to be a difficult two years of negotiations, she decided to go to the voters now. Polls suggest that the Conservative Party will easily win an election if it is held soon, thus strengthening her majority.

While the election will certainly reopen the debate over Brexit, the country remains on track to sever ties with the European Union. Under the current plan, Britain will officially leave in March 2019.

The Brexit referendum passed by a thin majority, and Mrs. May did not come to power through a general election. If she wins this vote, it will embolden her, adding to her legitimacy and strengthening her ability to withdraw from the union smoothly.

It is unlikely that the Conservatives will suffer significant losses or that there will be a new referendum on Brexit.

According to a BBC analysis of recent polls, the Conservatives are leading by 17 percent. But the polls in Britain have been wrong before, including before the Brexit referendum. If Mrs. May’s majority is reduced or the Conservatives somehow lose, then a new Brexit strategy, including a decision to remain in the European Union, becomes feasible.

The election presents considerable risks for the opposition Labour Party. Another bad loss might lead to an internal shake-up and the replacement of the party’s contentious leader, Jeremy Corbyn.

• Labour: Mr. Corbyn called the election a “chance to vote for a government that will put the interests of the majority first.” But his party is expected to lose many of the 229 seats it holds. If Labour performs better than expected, even if it loses seats, it may still be hailed as a victory.

• Scottish National Party: Nicola Sturgeon, the first minister of Scotland, called Mrs. May’s decision to seek an early election a “huge political miscalculation.” Scots overwhelmingly voted against Brexit, and Ms. Sturgeon has called for a referendum on Scottish independence, though a similar one was rejected in 2014.

• Liberal Democrats: The 2015 general election proved disastrous for the centrist, anti-Brexit Liberal Democrats, which had been a junior partner in a coalition government with the Conservatives. Since the Brexit vote, however, the Liberal Democrats say they have gained thousands of members. A strong showing could restore some of their former power, but it would be unlikely to reverse Brexit.

• U.K. Independence Party: The far-right, nationalist UKIP has no members in Parliament, but it was instrumental in swinging the Brexit referendum. Though it is a one-issue party that has seemingly seen that issue become national policy, picking up even a few seats could be a boon.