The Algeria international has signed a four-year deal with Laurent Blanc's side.
"Welcome Aouar," Al Ittihad posted on X.
The former Olympique Lyonnais player will join N'Golo Kante and Fabinho in the Al Ittihad midfield.
The midfielder played one game for France - a friendly against Ukraine in 2020 - before switching allegiance last year to Algeria, where his parents were born.