Former French President Nicolas Sarkozy has been elected head of the opposition UMP, in what is being seen as the start of a new bid for the presidency.
Mr Sarkozy gained 64.5% of the vote, well ahead of his nearest rival Bruno Le Maire.
He was under pressure to win by a wide margin, and hoped to get more than 70% to keep his re-election hopes alive.
The UMP has struggled to be effective in opposition to Francois Hollande, despite the president's dismal ratings.
Mr Sarkozy, 59, won 85% of the vote when he was first elected party leader in 2004.
He served as president from 2007 and 2012 but left active politics after his defeat to Mr Hollande.
More than 150,000 party members - over 50% - voted in the election, despite the process being slowed down by a cyber attack.
Mr Le Maire, a former agriculture minister, received just less than 29.2% and a third candidate, MP Herve Mariton 6.3%.
Mr Sarkozy posted a message to supporters on his Facebook page (in French).
"I would like to thank all the UMP members who did me the honour of electing me leader of our political family," he said.
"Their mobilisation, at a level unequalled in the history of our movement, is the best response to two years of internal quarrels and divisions."
But a spokeswoman for Mr Hollande's Socialist Party said that the UMP's campaign had provided "nothing new for France".
"Mr Sarkozy's victory in the campaign for the UMP presidency is not the triumphal return that he was hoping for," Corinne Narassiguin said.
Florian Philippot, spokesman for the far-right National Front, described the result as an "utter failure" for Mr Sarkozy.
The UMP will choose its nominee for the 2017 presidential elections in two years, but correspondents say a lower than expected party vote for Mr Sarkozy could encourage other UMP leaders to stand against him.
Former prime ministers Alain Juppe and Francois Fillon are widely reported to want to be the UMP's candidate for president.
Mr Sarkozy is disliked by some French voters for his unusually high-profile private life, with critics branding his one-term tenure as the "bling-bling" presidency.
The 2012 leadership ballot - after Mr Sarkozy left office - degenerated into a hugely damaging row as Mr Fillon refused to accept the victory of Sarkozy ally Jean-Francois Cope.
Declared the winner, Mr Cope stood down this May after the party suffered badly in the European elections as the National Front capitalised on voter discontent.
National Front leader Marine Le Pen is due to be returned unopposed as party leader at its meeting in Lyon on Sunday.