PARIS — Francois Fillon won France’s first-ever conservative presidential primary Sunday after promising drastic free-market reforms and a crackdown on immigration and Islamic extremism, beating a more moderate rival who had warned of encroaching populism.
‘‘President! President!’’ chanted the former prime minister’s supporters as he declared victory over Alain Juppe in a nationwide runoff election.
Polls suggest the 62-year-old Fillon, prime minister from 2007 to 2012 under then-president Nicolas Sarkozy, would have a good chance of winning the presidency in the April-May election.
Fillon campaigned on promises of slashing public spending, capping immigration, and supporting traditional family values and friendlier ties with Russian President Vladimir Putin. Fillon enjoyed a surprise surge in popularity in recent weeks over longtime front-runner Juppe, who also previously served as prime minister.
In a sober victory speech, Fillon promised to defend ‘‘French values’’ and said France needs ‘‘a complete change of software.’’
‘‘There is in our country an immense need for respect and pride. There is also a call for the authority of the state, and exemplary behavior by those who lead it,’’ he said.
Fillon, whom Juppe had accused of running a divisive campaign that catered to the far right, struck a slightly more inclusive tone Sunday night.
‘‘No one should feel excluded from a society that I want to see more just and with more solidarity,’’ he said.
Juppe, 71, congratulated Fillon on his ‘‘wide victory.’’ During the primary campaign, he expressed similar ideas as his rival on the French economy, but tried to rally conservatives around a more tolerant attitude toward France’s ethnic, religious, and social diversity.
Based on results from about 88 percent of polling stations, organizers of the center-right Republicans party primary said Fillon led with 67 percent of the vote, compared to 33 percent for Juppe.
Fillon’s toughest challenge is likely to be far-right leader Marine Le Pen. Le Pen is running an anti-establishment campaign that particularly targets immigrants, France’s large Muslim minority, and the European Union.
Socialist President Francois Hollande is expected to announce in the coming weeks whether he will seek reelection, but the French left has been weakened by Hollande’s extreme unpopularity.
Both Fillon and Juppe are high-profile leaders of the Republicans party who knocked their onetime boss, former president Nicolas Sarkozy, out of the primary’s first round of voting a week ago. Sarkozy then threw his weight behind Fillon.
Sunday’s runoff came after a bruising end phase to the monthslong primary contest, an American-style effort to end party infighting and bolster support for the party’s nominee. The conservatives previously chose their candidate internally.
Fillon, a conservative Catholic who opposed France’s law legalizing same-sex marriages, said he plans to reduce immigration ‘‘to a minimum’’ — positioning himself firmly to Juppe’s right.
Fillon wants to drop sanctions against Russia over its aggressive actions in Ukraine and partner with Russia in the fight against Islamic State extremists. Fillon insists ‘‘Russia poses no threat’’ to the West, while Juppe wants France to continue putting pressure on Putin on various fronts.
They both pledged to cut public spending, reduce the number of civil servants, raise the retirement age from 62 to 65, end the 35-hour workweek, and cut business taxes.
All French citizens over 18 — members of the Republicans party or not — were eligible to vote in the primary if they paid 2 euros and signed a pledge stating they ‘‘share the republican values of the right and the center.’’
With the Republican candidate in place, attention will now turn back to the ruling Socialist Party and the future of Hollande. Prime Minister Manuel Valls said in an interview published Sunday that he may seek the Socialist candidacy, though his boss is still considering his own bid for a second term.