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.
Belarus frees Nobel winner, protest figures as US lifts more sanctions
Belarusian President Alexander Lukashenko freed 123 prisoners on Saturday including Nobel Peace Prize winner Ales Bialiatski and leading opposition figure Maria Kalesnikava after two days of talks with an envoy for President Donald Trump, a US statement said.
Indonesia flood death toll exceeds 1,000
The death toll from floods and landslides that struck three provinces on Indonesia's Sumatra Island has exceeded 1,003, with 218 people still missing, according to the latest data released Saturday by the National Disaster Management Agency (BNPB).
Ukraine's Odesa suffers major blackouts after Russian attack
Ukraine's southern port city of Odesa and the surrounding region suffered major blackouts on Saturday after a large overnight Russian attack on the power grid across the country.
Two killed in Ukrainian drone strike on Russia's Saratov
Two people were killed overnight in a Ukrainian drone strike on the Russian city of Saratov, regional governor Roman Busargin said on Saturday.
Thailand continues Cambodia strikes despite Trump's ceasefire claim
Thailand's leader vowed to keep fighting on the disputed border with Cambodia as fighter jets struck targets on Saturday, hours after US President Donald Trump said he had brokered a ceasefire.
Turkish President Tayyip Erdogan, fresh from a meeting with Russia's Vladimir Putin, said he hopes to discuss a Ukraine-Russia peace plan with US President Donald Trump, adding that "peace is not far away".
His Highness Sheikh Abdullah bin Zayed Al Nahyan, UAE Deputy Prime Minister and Minister of Foreign Affairs, and Serbia’s Foreign Minister Marko Đurić. have agreed to deepen political coordination after signing a Memorandum of Understanding (MoU) during talks in Abu Dhabi.
The UAE has introduced changes to its laws governing the care of children of unknown parentage, expanding custody options and strengthening child protection measures.
