In N'Djamena on Saturday and Niger's capital Niamey on Sunday, Valls will hold talks with respective presidents Idriss Deby and Mahamadou Issoufou.
Accompanied by his defence minister Jean-Yves Le Drian, Valls will on Saturday also visit a French military base near N'Djamena airport to meet troops who form part of the regional Barkhane anti-Islamist force.
For the French army, N'Djamena is a strategic point in the fight against Boko Haram Islamist fighters operating just tens of kilometres away in northeast Nigeria.
French troops intervened in Mali in January 2013 to chase out hardline Islamists, including Al-Qaeda in the Islamic Maghreb, which had seized control of the country's northern desert cities.
This intervention was replaced several months ago by a wider counter-terrorism operation, codenamed Barkhane, in five countries along the southern rim of the Sahara — Chad, Niger, Mali, Mauritania and Burkina Faso.
French President Francois Hollande made similar trips to Chad and Niger in July.
The Barkhane force — named after a crescent-shaped sand dune in the desert — currently includes 3,200 French troops, plus special forces personnel, according to a government source.