Alain Juppe has conceded defeat in France's first-ever conservative presidential primary, congratulating rival Francois Fillon for a "wide victory".

Former prime minister Juppe, who had long been considered the favorite for the primary, made the concession announcement after results from Sunday's runoff election showed him collecting 32 percent of the vote to Fillon's 68 percent.

Juppe said he will support Fillon in the French presidential election in April and May.

"I finish this campaign as I began it, as a free man who did not compromise what he is or what he thinks," he said in Paris on Sunday night.

Juppe is calling for unity and calm after a campaign in which he has accused Fillon of pandering to the anti-immigrant, anti-Islam far right.