Voters in France will cast ballots on Sunday in the final round of snap legislative elections. The results could force President Emmanuel Macron to govern alongside far-right opponents or usher in chronic political instability weeks before the Paris Summer Olympics.

Mr. Macron called the elections for the 577-seat National Assembly, France’s lower and more prominent house of Parliament, last month in a risky gamble that appeared to have largely backfired after the first round of voting last week.

Most polls close at 6 p.m. local time on Sunday, or as late as 8 p.m. in larger cities. Nationwide seat projections by polling institutes, based on preliminary results, are expected just after 8 p.m. Official results will come in throughout the night.

Here is what to watch for.

Will the far right win enough seats for an absolute majority?

That will be the key question.

The first round of voting was dominated by the nationalist, anti-immigration National Rally party. An alliance of left-wing parties called the New Popular Front came in a strong second, while Mr. Macron’s party and its allies came in third.

Seventy-six seats were won outright — roughly half by the National Rally. But the rest went to runoffs.

Over 300 districts were three-way races until over 200 candidates from left-wing parties and Mr. Macron’s centrist coalition pulled out to avoid splitting the vote and try to prevent the far right from winning.