Galtier left PSG this summer after just one season in charge during which he won the Ligue 1 title and the Trophee Des Champions trophy at the Parc Des Princes.
Al Duhail parted company with former Argentina striker Hernan Crespo on Wednesday.
Crespo led Al Duhail to the Qatar Stars League title last season but have endured an indifferent start to the season, sitting fifth on the domestic league table and third in their Asian Champions League group.
Al Duhail have not specified the length of contract handed out to Galtier.
The Frenchman will begin his reign with matches against Al Gharafa and Cristiano Ronaldo's Al Nassr in the coming weeks.
Galtier can count on former Liverpool and Barcelona forward Philippe Coutinho among the players who can inspire a quick turnaround in fortunes for his new side.
