The 41-year-old Englishman succeeds Antoine Kombouare, who guided the club to an 11th-placed finish last season.
"Liam Rosenior brings together all the qualities we were looking for," Sporting Director Marco Neppe said in a statement.
"He is a modern, demanding coach and recognised for his ability to help both the players and the team progress. Beyond his tactical skills, we were particularly attracted by his management qualities and his ability to unite a group around a clear vision."
Rosenior returns to French football after leaving RC Strasbourg, whom he managed from 2024 to 2026 before taking charge of Chelsea in January following Enzo Maresca's departure.
His spell at Stamford Bridge proved short-lived, with the club ending his contract in less than four months despite handing him a deal that ran until 2032.
Paris FC said Rosenior will begin work on Thursday.