What to Watch For in France’s High-Stakes Elections

France is heading to the polls on Sunday for the first round of snap legislative elections that President Emmanuel Macron unexpectedly called this month, a gamble that has thrust the country into deep uncertainty over its future.

Voters are choosing their 577 representatives in the National Assembly, the country’s lower and more prominent house of Parliament, which will determine the future of Mr. Macron’s second term.

A new majority of lawmakers opposed to Mr. Macron would force him to appoint a political opponent as prime minister, radically shifting France’s domestic policy and muddling its foreign policy. If no clear majority emerges, the country could be headed for months of turmoil or political deadlock. Mr. Macron, who has ruled out resigning, cannot call new legislative elections for another year.

France’s nationalist, anti-immigrant National Rally party is widely expected to dominate the race. A broad alliance of left-wing parties could come in second. Mr. Macron’s centrist Renaissance party and its allies are expected to lose many seats.

Most polls will close at 6 p.m. local time on Sunday, or as late as 8 p.m. in larger cities. Nationwide voting projections provided by polling institutes, based on preliminary results, are expected right after 8 p.m. and are usually reliable. Official results, published by the Interior Ministry, will come in throughout the night.

Here is what to expect.

The voting happens in two rounds, and participation is expected to be high.

France’s 577 electoral districts — one for each seat — cover the mainland, overseas departments and territories, and French citizens living abroad. In each district, the seat is awarded to the candidate who gets the most votes.