PARIS — French voters chose a socially conservative, budget-cutting former prime minister on Sunday to lead the center-right Republican Party in next year’s presidential election. Once again, the outcome upset pollsters’ initial predictions, and it paved the way for a likely face-off with the country’s far-right party in 2017.

François Fillon, 62, a sober, dark-suited government veteran who called for economic sacrifice, major changes in the French workplace and a crackdown on immigration and Islam, won about 67 percent of the vote in the primary contest on Sunday, crushing his more centrist opponent, Alain Juppé, who is also a former prime minister.

French presidential elections are usually decided in two rounds, with the first round winnowing the field to two candidates. Having won his party’s primary, Mr. Fillon is widely expected to be one of those two finalists in the general election in the spring.

It now seems increasingly unlikely that the current governing party, the Socialists, will produce the other. The French left is weak and in disarray after five years in which high unemployment rates and slow economic growth have barely budged. President François Hollande has not said whether he will run for another term, and many in his party hope he does not.