Marquinhos bundled home four minutes before the break to give the hosts reward for a strong first half.
And when Cavani notched his fourth goal of the season from the penalty spot after coming off the bench the win was secured, as PSG put the pressure back on rivals Monaco at the summit.
The hosts rested players ahead of their midweek UEFA Champions League clash against Benfica in a busy fixture schedule for the Parisiens, leaving out Ezequiel Lavezzi, Cavani and Javier Pastore in attack, with Alex and Thiago Silva missing out through injury.
Knowing that a win would take them above Monaco in the table, the hosts looked to dominate the early proceedings, but it was Toulouse who created the first chance after five minutes with Etienne Didot forcing a save from Salvatore Sirigu down to his left from a strong header.
Thiago Motta's eighth-minute strike was PSG's first look at the Toulouse goal, but the Italian's shot was off target.
PSG failed to create another clear opening until the 23rd minute when captain Zlatan Ibrahimovic turned Steeve Yago on the edge of the area, only to see his shot fly wide of the left-hand post.
Toulouse's defensive game plan appeared to be stifling PSG, although they threatened again after half an hour when Lucas Moura's free-kick forced a corner, and Motta's flag-kick saw strong handball appeals turned down.
After 40 minutes, PSG found their breakthrough.
Motta's whipped free-kick into the box was headed goalwards towards Marquinhos, who bundled the ball home at the second attempt despite a good initial save from Ali Ahamada.
Toulouse almost levelled instantly as Aymen Abdennour saw his side-footed strike cleared off the line by Marco Verratti in first-half injury time.
PSG boss Laurent Blanc made his first change 10 minutes after the break, introducing Lavezzi for Jeremy Menez after a quiet opening to the half that saw Isiagga Sylla work goalkeeper Sirigu.
The hosts threatened to double their lead on the hour mark as Ibrahimovic was played through, but the Swede saw his shot hit the side netting. Lucas Moura then had another chance four minutes later saved by Ahamada.
Three minutes later, they struck the post - with Adrien Rabiot unfortunate to see his header hit the woodwork - and Blanc reacted by bringing on Cavani for Ibrahimovic.
Clement Chantome’s half volley showed Toulouse were still capable of taking a point on the counter but Cavani then made his impact with 11 minutes left, winning a penalty himself when he was brought down in the box by Uros Spajic, and he calmly slotted home the spot-kick to seal the points.
