French fans were in full voice on Court Philippe Chatrier as Mahut and Herbert comfortably won the opening set.
The second set was closer as Austrian Marach and Croatian Pavic broke back, having dropped serve in the seventh game, and forced the set into a tiebreaker.
Mahut and Herbert held their nerve though and took the tiebreak when Herbert punched away a volley to spark wild celebrations from the pair who had previously won the 2015 U.S. Open and 2016 Wimbledon.
The only other all-French pairs to win the men's doubles at Roland Garros were Julien Benneteau and Edouard Roger-Vasselin in 2014 and Henri Leconte and Yannick Noah in 1984.
Noah, France's Davis Cup captain, watched from the stands, joining in the home celebrations.
(Reporting by Martyn Herman; Editing by Clare Fallon)
