There currently is one option to travel by night train from Paris (France) to Tarbes (France), taking between approximately 10 and 12 hours: Namely the INTERCITES DE NUIT n° 3731 operated by SNCF.
In France, a few night train lines are operated by the state-owned SNCF.
SNCF night trains are equipped with standard seating carriages and couchette carriages offered in two comfort classes.
Couchette carriages generally have 4-person compartments in first class and 6-person compartments in second class. The berths are simply designed in both classes and are about 1.9 meters long.
Yes, they are available. You can book an entire couchette compartment for private use. This can also be done for a group.
In first class, only four people share a compartment, the berths are wider, and travelers have access to station showers in Paris and Toulouse. Second class accommodates six people per compartment and allows bicycles to be brought for an additional fee of 10 euros – a plus for cyclists.
You should bring your own food as there is no restaurant on board. Alternatively, you can pre-order meals and drinks or eat before departure. First class travelers receive a small breakfast. Each passenger receives a night kit with refreshing towelette, dental cleaning tablet, sleep mask, earplugs, and water.