Toulon opened the scoring through a Jonny Wilkinson penalty, but Montpellier soon took control of the match, preventing the visitors from adding further to their score.
A try and three penalties gave the hosts a comfortable lead at half time, helped by Toulon being reduced the 14 men for a time when Delon Armitage was sin-binned.
Benoit Paillaugue added a try early in the second half to effectively seal the game for Montpellier, with Toulon offering little in the way of attack.
As the game went on, the hosts substituted a number of their starters, allowing their fringe players some time on the field.
Toulon have won all five of their previous games during the pool stage of the competition.