The home side had never previously beaten PSG in eight top-flight attempts and it appeared the game would run true to form when they found themselves a goal down through Kylian Mbappe's clinical strike.
But Thomas Tuchel's side were guilty of coasting when in front and were made to pay by strikes from Mounir Chouiar and Jhonder Cadiz either side of half-time.
PSG twice hit the frame of the goal and missed a glut of late chances as they went in search of a leveller that did not arrive, meaning just a third loss of the season in all competitions.
Despite an 18-point deficit between the teams prior to kick-off, bottom club Dijon started the match brightly and tested Keylor Navas through efforts from Julio Tavares and Cadiz.
However, Mbappe gave the visitors the lead against the run of play, delicately lifting the ball over Alfred Gomis after being put in the clear by Angel Di Maria.
But PSG struggled to get going and were pegged back on the brink of half-time, Navas spilling Didier Ndong's low cross into the path of Chouiar for a close-range finish.
Picking up from where they left off, Dijon scored a second 103 seconds into the second half, Cadiz turning Marquinhos before firing the ball through the legs of goalkeeper Navas.
Di Maria squandered two good opportunities to draw PSG level and Mauro Icardi guided a header against the crossbar from six yards.
Leandro Paredes also hit a post with a drive through a sea of bodies but, despite the introduction of Edinson Cavani, there was no way through a resolute Dijon defence.
What does it mean? PSG believe their own hype
PSG had won four league games in a row prior to this match, scoring exactly four times in each of the last three.
They simply did not turn up today, though, and can have few complaints, albeit they still eight points clear of Nantes, who travel to Bordeaux on Sunday.
Cadiz causes chaos
Tuchel will be furious with the manner of both Dijon goals, with the second particularly preventable.
Cadiz was allowed to get a shot away inside the box unchallenged for what proved to be the winner - one of three attempts on target he managed across the game.
A game to forget for Navas
PSG were looking comfortable as half-time approached, only for Navas to spill a routine cross to gift Chouiar a goal and Dijon a route back into the match.
The former Real Madrid keeper was then let down by his defenders for the second, though he hardly covered himself in glory with his attempt to keep out Cadiz's low shot.
PSG host Club Brugge in the Champions League on Wednesday and return to Ligue 1 action with a trip to Brest on Saturday, the same day Dijon - who have moved off the foot of the table - travel to Monaco.