French Interior Minister Bernard Cazeneuve has been named as prime minister, replacing Manuel Valls, who resigned in order to make a bid for the presidency next year.
Mr Valls presented his resignation to President Francois Hollande on Tuesday.
Mr Cazeneuve will be in charge of the Socialist government until June’s parliamentary elections.
He has played a key role in managing France’s security since the jihadist terror attacks in Paris last year.
Mr Valls will face other contenders in the Socialist primary next month.
Last week, in a move that surprised many, President Hollande announced that he would not seek a second term.
He is the first president since France’s Fifth Republic was created in 1958 not to seek a second mandate. But he has haemorrhaged support amid stubbornly high unemployment and anxiety about Islamist terror.
If successful, Mr Valls will face Francois Fillon and Marine Le Pen in the first round of the presidential election in April.