The hosts were beaten for the second game in a row, severely denting their Champions League ambitions as Alain Casanova's men recorded a third straight win
Aymen Abdennour's 66th minute goal settled the contest, which was a largely uninspiring affair as the side from the Pink City won a third straight league game, and a first against Marseille since 2007, to boost their own European ambitions.
Marseille were without Mathieu Valbuena after the winger picked up a knock on international duty in midweek, although they were boosted by the return of Andre Ayew.
However, it would be the visitors who enjoyed the best of the opening chances created on the south coast. Etienne Capoue, latching onto Etienne Didot's pass, saw his right-footed effort flash wide as OM were given an early scare. That continued minutes later when Emmanuel Riviere fired over from Cheikh M'Bengue's cross.
Eventually, Didier Deschamps' men found their rhythm through Andre Ayew and Morgan Amalfitano. The latter, in the running for the league's Player of the Month attempted a shot which failed to trouble Ali Ahamada in the Toulouse goal, before younger brother Jordan Ayew wasted a good opening created from Jeremy Morel's drilled cross.
Perhaps the best chance of a rather meagre first half fell to Abdennour. The Tunisian international rose highest to meet Capoue's cross, but narrowly directed wide of Steve Mandanda's goal.
The first half was notable for profligate finishing from both sides, though OM did have a penalty appeal turned down after Capoue appeared to have handled, but a second viewing put that allegation to rest as the sides entered the interval at 0-0 with the hosts rather more frustrated at their inability to strike a blow.
The second half commenced in the same nature as the first, with Marseille building possession but wasteful when it mattered. At the other end, Adrien Regattin threatened with an effort against Mandanda, though both men would engage in a slight argument which briefly halted proceedings.
Alain Casanova's men were at this point gaining the upper hand. Serge Aurier raced through the flanks before locating Etienne Didot with a fine pass. The midfielder fired towards Mandanda, who thwarted the visitors with a fine block.
From the following corner however, Marseille's luck would run out. Abdennour again was left unmarked and he powered a header over Cesar Azpilicueta and into the net after 66 minutes.
The home side attempted to issue a response, but were largely kept at bay by le Tefece's resolute backline. Brandao headed into the path of Amalfitano, whose volley was far too tame to cause Ahamada any problems.
L'OM were rather susceptible at the back from set-piece situations, and their defensive frailties were almost exposed again from a corner, though this time Capoue fired agonisingly wide as a static defence breathed a sigh of relief. Rod Fanni later saw a low effort easily saved, a testament to the balance of play as the match petered out.
Following the defeat, Marseille drop to eighth on 39 points, eight behind Lille in third, who drew 2-2 with Auxerre. However, Didier Deschamps' men do have a game in hand on Wednesday, against Evian. Toulouse move to fifth, with 43 points.