The Uruguayan, who had missed the last five games through injury, marked his return in the perfect fashion as PSG moved eight points clear at the top of Ligue 1 following Monaco's surprise 2-0 defeat to Saint-Etienne.
Laurent Blanc's men now boast home and away league wins over their arch rivals as they continue to dominate the French top flight.
Brazilian defender Maxwell, a scorer in the 2-1 win in the reverse fixture at the Stade Velodrome back in October, proved to be a thorn in Marseille's side once more as he opened the scoring five minutes into the second half - an ideal way to celebrate signing a contract extension during the week.
And a superb performance from the champions was capped off 12 minutes from time when Cavani came off the bench to head home his 21st goal of the campaign - in the process putting PSG within touching distance of a second consecutive Ligue 1 title.
Cavani was left out of the starting XI despite having returned to full fitness following a thigh injury, but the hosts still offered plenty of firepower and they should have taken the lead six minutes in when Ezequiel Lavezzi wasted a glorious opportunity.
The Argentinian was played through by Lucas Moura but, instead of squaring the ball to Zlatan Ibrahimovic, he rounded goalkeeper Steve Mandanda and sent his shot narrowly wide of the post.
Marseille did not heed that early warning, though, and they were grateful to defender Rod Fanni for clearing Lucas' effort off the line after the winger had beaten several defenders - Fanni denying the Brazil international a spectacular solo goal.
The visitors did offer a sporadic attacking threat of their own, midfielder Mathieu Valbuena forcing PSG goalkeeper Salvatore Sirigu into a strong diving save with a curling strike from the edge of the area before half-time.
Chances were few and far between towards the end of what became an increasingly scrappy first half, although Ibrahimovic went close just before the break with a header from Lavezzi's left-wing cross.
But the breakthrough finally arrived almost immediately following the restart as Maxwell slotted a composed finish underneath Mandanda after being played through by Ibrahimovic.
Jose Anigo's side offered little in response and were consistently on the back foot as they struggled to create goalscoring opportunities.
Cavani's introduction came in the 70th minute and the former Napoli man did not take long to find the net, converting with a bullet header from Gregory van der Wiel's right-wing delivery.
Ibrahimovic then missed the chance to add gloss to the scoreline with a lofted finish, but that proved to be little more than a footnote in a superb win for PSG.
