Their form on the road has been to Marseille's detriment in their bid to win the championship for a 10th time, but Marcelo Bielsa's men showed no signs of travel sickness this time around at the Stadium Municipal.
The triumph takes them above PSG – who face Lens on Saturday – on goal difference and puts them a point adrift of leaders Lyon.
In-form forward Michy Batshuayi put the visitors ahead in the second minute with a fine curling finish into the bottom-left corner from the edge of the area.
Marseille soon doubled their lead as Baptiste Aloe deflected Benjamin Mendy's powerful drive beyond Zacharie Boucher.
Toulouse defender Jacques Moubandje then inadvertently turned home Andre Ayew's left-wing cross to make it 3-0 after just 20 minutes.
The game was all but ended as a contest when Batshuayi capped off a quick Marseille counter in the 44th minute.
Alain Casanova had been given the dreaded vote of confidence earlier in the week, and his side showed signs of spirit in the second half as Wissam Ben Yedder pulled one back with a neat low finish in the 76th minute.
But that only served to further motivate Marseille, who rounded off the rout as Ayew and Andre-Pierre Gignac netted to heap misery on the relegation-threatened hosts.
