LONDON — Less than 12 months after deciding to quit the European Union, Britons will vote on many of the same questions again, after lawmakers on Wednesday agreed to call an early general election, the outcome of which could shape Britain’s relations with its closest neighbors for decades to come.

By an overwhelming vote of 522 to 13, British lawmakers agreed to hold elections on June 8 at the request of Prime Minister Theresa May, who hopes to strengthen her parliamentary support and gain a freer hand to negotiate Britain’s withdrawal from the bloc.

The outcome of Wednesday’s vote in Parliament was never in doubt, even with the requirement of a two-thirds threshold to call a snap election that, until Tuesday morning, Mrs. May and her aides had insisted would not happen.

Electioneering was already underway during the parliamentary debate, with party leaders exchanging insults, as well as highlighting some of the thorniest issues Britain faces today. Those include the clarity of Britain’s break with the European Union, the stark inequality among the country’s regions and the future of Scotland, where there are growing calls for a new referendum on independence.