There are a number of train routes from France to Spain. On this page you will find details of these routes as well as details of how to book your train from France to Spain.
The Best Way to Get from France to Spain
From December 2013, there is now a high-speed train from Paris to Barcelona that connects you in just six hours and twenty minutes.
This is the quickest route, even if traveling from Madrid. From Madrid you need to change at present in Figueres or Barcelona, but direct routes are no doubt imminent.
Rail Passes for France and Spain
If you plan on traveling a lot by train in France and Spain, you should consider a Eurail France-Spain Pass. This rail passes offers four to ten days of unlimited train travel in France and Spain.
Trains from France to Spain with Elipsos
Elipsos is the name of the 'train hotel' overnight sleeper service from Madrid to Paris via Orleans, Blois, Poitiers, Vitoria, Burgos and Valladolid. The Elipsos website is chaotic (one might say 'broken'). I would not recommend using this service.