Since the month of July, Mont de Marsan is accessible in 3h43 from Paris.
From Bordeaux - Gare Saint Jean (direct link): 1h30
>> see schedules HERE
You can reach Mont de Marsan by TGV by Dax train station and then take the RDTL bus service which connects Dax to Mont de Marsan from Monday to Saturday.
Due to the many changes in SNCF timetables in France, we advise you to go to the following site: www.sncf.com/