Despite the modest scoreline, the Ligue 1 champions were dominant against their opponents, who are currently fighting relegation from the third tier of French football.
Nonetheless, Les Herbiers gave a positive account of themselves against the nation's standout side and remained in the game until well into the second half.
However, the deadlock was broken on 24 minutes through Lo Celso, who was given space and time to rifle a 25-yard effort beyond Matthieu Pichot and into the back of the net.
PSG continued to press after the restart but could not put the game out of sight come the break.
Mbappe had the ball in the back of the net on 50 minutes, but the referee consulted VAR and adjudged Marquinhos to have handled the ball in the build-up, thus disallowing the goal.
Cavani stepped up and duly put his side two goals up by drilling his spot kick into the bottom corner of the net from 12 yards.
With Les Herbiers unable to find a response, the final whistle saw PSG win their fourth Coupe de France in a row and add the trophy to their Ligue 1 and Coupe de la Ligue haul for the season.
PSG (4-3-3): Trapp; Alves (Meunier 86'), Silva, Marquinhos, Berchiche; Lo Celso, Motta (Draxler 68'), Rabiot; Mbappe (Pastore 86'), Di Maria, Cavani
LES HERBIERS (4-2-3-1): Pichot; Marie, Fofana, Dequaire, Pagerie; Flochon, Eickmayer (Couturier 88'); Bongongui, Vanbaleghem (Dabasse 62'), Rocheteau; Germann (Gboho 63')