Bernard Cazeneuve has been appointed as the new Prime Minister of France after Manuel Valls quit his post to focus on running as President in the country's coming elections.
He will be seeking the Socialist nomination for the vote, hoping to pit himself against conservative candidate Francois Fillon and Marine Le Pen, leader of the far-right Front National.
"I have appointed Mr Cazeneuve as Prime Minister and charged him with forming a new government," said President Francois Hollande, who will not be running for re-election.
The 53-year-old is a close ally of Mr Hollande and has become a popular figure in French politics as the champion of measures tackling extremism.
Since being appointed interior minister in 2014 he has led the response to a series of terror attacks claiming more than 200 lives, championing counterterrorism and intelligence laws and implementing the country's continuing state of emergency.
Mr Valls, who survived a vote of no confidence earlier this year, has been criticised by members of his own party for supporting controversial labour reforms and burkini bans, and is known for his outspoken, authoritarian style and his tough views on immigration and security.
He will face other contenders in the Socialist primary next month before France's two-part presidential election in April and May.
An opinion poll published on Tuesday forecast that Mr Fillon would beat Ms Le Pen in the second round of the presidential election with 65 per cent of the vote.
The Ifop-Fiducial poll for iTele, Paris Match and Sud Radio also said that no candidate from the Socialist party would do better than a fifth placed-score. The survey was taken before Mr Valls put his name forward.
His party holds a majority in France's National Assembly but its popularity has been severely damaged by the refugee crisis and the government's inability to prevent a succession of terrorist attacks.
Additional reporting by agencies
