France's conservative The Republicans party on Saturday chose the moderate chief of the Paris region Valerie Pecresse to challenge President Emmanuel Macron in the elections next year.
Pecresse won almost 61 percent of the vote among party members while Eric Ciotti won just over 39 percent, party leader Christian Jacob said.
Both had made the run-off after the first round of voting earlier this week upended expectations.
Ciotti accepted defeat and immediately pledged to support Pecresse and called for her to fight "Macronism", referring to her future rival.
She is the first-ever female presidential candidate of the The Republicans (LR) conservative party and presents herself as a voice of moderation, over hardliner Ciotti.
The favourites ex-minister Xavier Bertrand and former EU Brexit negotiator Michel Barnier were both knocked out and went on to back Pecresse.
"The party of (France's post-war leader) General (Charles) de Gaulle... our political family, will have a female candidate in the presidential election. I am thinking of all the women of France today. I will give everything to triumph," she said after the result was announced.
"Today, everything begins and I want to raise hopes. On Monday I will begin my tour of France, starting in the Vésubie valley," she announced.
"Nothing is lost. We are not condemned neither to disorder nor decline. Ou country is full of talent and energy."
The result is being keenly watched by the Elysee.
While all opinion polls have predicted centrist Macron should win the election, the emergence of a strong candidate on the traditional right who gains momentum during the campaign would be a major factor.
The campaign has so far been waged on the right, with Macron's government tacking rightwards over the last months with tough rhetoric on immigration and preserving France's secular system.
The Republicans failed to make the run-off in 2017, after its candidate Francois Fillon was felled by a graft scandal.
But the party, out of power since 2012, makes much of its status as the inheritor of the presidencies of Nicolas Sarkozy and Jacques Chirac as well as Charles de Gaulle.
"The Republican right-wing is back. It will fight with implacable will. France cannot wait any more," Pecresse said, promising to make France "respected in the world".
Striking the tone for her campaign, she added: "I understand the anger of a people who feel powerless against violence, Islamist separatism and uncontrolled immigration."
"I will not have a wavering hand against the enemies of the Republic," she added.
Ciotti has long argued for radical policy "disruptions" to protect a France he deemed at risk of losing its identity from immigration and economic decline, promising a "French Guantanamo" to hold suspected terrorists.
His rhetoric sometimes echoed that of the far-right pundit Eric Zemmour, who declared his candidacy this week. Ciotti said he would vote for Zemmour in a run-off against Macron.
The announcement of the Republicans candidate means that the main contours for the April 2022 election are largely set.
Macron has yet to declare but is widely expected to seek re-election. Analysts believe he may wait several more weeks before showing his hand to stay above the fray of day-to-day politics.
His main rival in the 2017 election, far-right leader Marine Le Pen, is standing again, while Zemmour's candidacy is a wild card that could yet have a major impact or simply fizzle out.
The left remains mired in disunity and communication problems, with the campaigns of the Socialist candidate, Paris mayor Anne Hidalgo, and Green candidate Yannick Jadot failing to make an impact. Both risk being outpolled by far-left leader Jean-Luc Melenchon.