The Brazil forward struck in the 68th minute to put PSG on 65 points from 25 games with arch-rivals and second-placed Olympique de Marseille on 52 after a 2-2 draw at St Etienne on Friday.
Monaco will take second place if they win at Angers later on Saturday (1900GMT).
Toulouse, who are 15th on 26 points and only one point above safety, held firm in the first half thanks to a spirited performance by keeper Alban Lafont.
But like most of PSG’s opponents this season, they eventually cracked even if coach Unai Emery had rested top striker Edinson Cavani ahead of Wednesday’s Champions League last-16 clash at Real Madrid.
Neymar collected Angel Di Maria’s cross and found the back of the net as his curled shot was slightly deflected by Toulouse captain Issa Diop.
He came close to doubling the tally 10 minutes later but his right-foot effort crashed on to the post.
Neymar hit the woodwork again in the 80th when his shot struck Lafont’s crossbar as PSG finished strongly.