Tron was forced to resign as junior minister for the civil service in 2011 over the allegations made by two women who worked for him when he was mayor of the southern Paris suburb of Draveil.
The women - Virginie Ettel, 41, and Eva Loubrieu, 44 - accused the 61-year-old and his former deputy, Brigitte Gruel, of abusing them during foot reflexology sessions that turned into threesomes in Tron's office between 2007 and 2010.
They said they submitted to be being groped and penetrated digitally for fear of losing their jobs.
The court found no evidence of coercion, despite noting "Georges Tron's clear ability to get his own way and to exert pressure".
Ettel later resigned, while Loubrieu was fired after being accused of theft.
The court's ruling said the pair appeared motivated by a desire for "vengeance."