Eric Béchu - who was co-coach with Galthié - will now take charge of the club's high performance division and its academy in particular.
Montpellier have been drawn in Pool 6 of next season's Heineken Cup along with Cardiff Blues, Toulon and Sale Sharks.
Meanwhile, it has been reported that former Italy and Stade Français playmaker Diego Dominguez is set to return to the Parisian club in a consultancy role.
Dominguez won four French titles in his seven years at Stade and now returns to join former team-mate Richard Pool-Jones' back-room staff as part of the same restructuring that saw Ledesma's departure from the Paris.
The 46-year-old will work with the club's kickers, while mentoring the young talent coming through the ranks.