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.
Israeli strikes kill 26 in Gaza, health officials say
Israel carried out its heaviest airstrikes in Gaza in weeks on Saturday, killing 26 people according to local health authorities, in attacks on a Hamas-run police station and on apartments and tents in an area sheltering displaced Palestinians.
US government starts likely brief shutdown as House fails to approve deal
The US government entered what is expected to be a brief shutdown on Saturday after Congress failed to approve a deal to keep a wide swath of operations funded ahead of a midnight deadline.
Thousands demonstrate in Minnesota and across US to protest ICE
Thousands of protesters took to the streets in Minneapolis and students across the United States staged walkouts on Friday to demand the withdrawal of federal immigration agents from Minnesota following the fatal shootings of two US citizens.
France tightens infant milk rules after recalls
France has lowered the safety limit for cereulide toxin in infant formula, aiming to strengthen protections after several major groups ordered worldwide recalls over contamination concerns, the farm ministry said on Saturday.
Fuel prices in the UAE will drop for a second consecutive month in February.
The UAE has reopened the newly renovated Sheikh Zayed Child Care Complex in Istanbul that can now accommodate and provide essential care for around 700 children.
UAE President His Highness Sheikh Mohamed bin Zayed Al Nahyan has held a phone call with Iranian President Dr. Masoud Pezeshkian.
