Driving St. Tropez to Paris

The driving itself is easy, because for a journey this long, you will have to take the motorway (A8-A7-A6).
The easiest road to the motorway is around the gulf to Sainte Maxime, then north to Le Muy. The seemingly more direct road through La Garde Freinet is very twisty, and the road through Toulon is prone to heavy traffic at all times due to construction work lasting until...2025.

However, this is a ten-hour drive (in perfect conditions)! If you are the only driver, it is bordering on the unsafe. I routinely drive from Paris to Toulon and back, and that 9-hour trip is barely OK when it's sunny, but thoroughly exhausting if there's rain on the way.

A MUCH better option would be to drive from St Tropez to Aix en Provence TGV (about 2 hours), return the car there, and take the fast train to Paris (3 hours). You'll save about 4 hours and a lot of stress. Also, train tickets for up to 2-3 people are cheaper than gas+tolls to Paris.

If you do take the train, which is wise advice from Balso, go onto SNCF connect before August 29th. The Senior Pass is on sale for 25euros until the 29th, instead of the 49 euro regular price. You discount on your Aix-Paris ticket would exceed the cost of the Senior Pass.