The list of candidates was officially confirmed today.
With Socialist President Francois Hollande's deep unpopularity leaving the left in disarray, and the far-right National Front flagbearer Marine Le Pen riding high in the polls, the rightwing candidate is thought to stand a good chance of snatching the presidency in a runoff vote in May 2017.
Alain Juppe, 71, the current favourite in the primary race, is a former prime minister who is seen as a moderate, notably on immigration, and is campaigning as a unifier.
Juppe returned from political exile after a party finance scandal that saw him convicted in 2004, winning back his long-time post as mayor of Bordeaux in 2006.
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Now viewed as an elder statesman, he has become one of the country's most popular politicians two decades after his reform agenda sparked the largest social movement France had seen since May 1968.
Juppe pledges to achieve "full employment" for France and to pull the country out of "stagnation" by tapping its under-utilised strengths and boosting education.
His tough talk on security and national identity has endeared him to many conservatives but made him a figure of hate on the left.
The son of a Hungarian immigrant father, Sarkozy was elected in 2007 on a promise to reform the ailing French economy.
But his taste for the high life soon cost him support, with voters casting him out after a single five-year term.
Two years later Sarkozy returned to head the opposition Republicans, a position he has used to try win back the presidency.
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