It's after the resignation of Edouard Philippe who has been in the post for three years.
Mr Castex, 55, is relatively unknown in France, although he is a senior civil servant.
The new Prime Minister has been a key player in the government's response to the Covid-19 pandemic.
Venezuela quake death toll nears 3,000 as rescue effort winds down
The death toll from last week's devastating twin earthquakes in Venezuela has climbed to 2,954, as hopes of finding more survivors continue to fade.
Eight injured in New York shooting
Eight people, including four children, were injured in a shooting in the Coney Island area of Brooklyn, New York City, last night as Independence Day celebrations and fireworks displays were taking place.
Trump appears on National Mall for July 4 speech after storm-related delay
After a storm-related delay, US President Donald Trump took the stage on the National Mall on Saturday to deliver a campaign-style speech to mark the country's 250th anniversary.
Qatar says all maritime activities will resume immediately
Qatar said on Sunday that maritime activities would resume with immediate effect, according to a Transport Ministry statement posted on X.
St. Petersburg region port, oil terminal hit in Ukrainian drone attack
Russia's second city of St. Petersburg and the surrounding Leningrad region came under a large Ukrainian drone attack overnight on Saturday, with a local port and oil infrastructure struck, Russian and Ukrainian authorities said.
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