Sarkozy had been widely expected to win the Union for a Popular Movement leadership in the vote by party members Saturday. The 59-year-old Gaullist collected 64.5 percent of the vote to defeat former government ministers Bruno Le Maire and Herve Mariton a margin that some analysts said was below expectations.
Still, the victory advances Sarkozy's hopes of running in the 2017 presidential race, and cements his return to the political scene after all but disappearing following his loss to Socialist Francois Hollande in the presidential election over two years ago.
Nearly 270,000 dues-paying party members were eligible to vote today.
The online system used came under an "organized" cyberattack that temporarily slowed down voting, UMP secretary-general Luc Chatel told France-Info radio on today.
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He said the party was filing legal action against the unidentified hackers behind the attack, and that police were investigating.
Sarkozy has used the UMP leadership as a springboard before: He also won it in 2004 with 85 percent of the vote - and built a ground game that helped propel him to victory in the presidential race three years later.