You did not specify which train, but for reservations in the TGV or AVE from France to Spain, do not wait until the day of travel. These trains usually sell out for passholders several days in advance. Especially around weekends and certainly around long weekends such as this one.

So it's quite possible that the 10:10 TGV from Paris to Barcelona does not have pass holder seats left. Same for the later journey with a change in Valence TGV.

Alternative is a journey via Portbou, e.g.:

The earlier departure from Paris at 8:12 is already fully booked. The 11:11 TGV to Perpignan still has 51€ seats left in 1st class (this is possible with a pass in 2nd class). The other trains (TER / R) don't need a reservation.

TGVs in France or from France to Spain can be booked by phone via SNCF. Press #85 for English, no booking fee, reservations are sent via ee-mail.

Paris - Barcelona is one of the worse Routes for Railpasses as the seats are limited and often sold out days if not weeks in advance I recommend to try to reserve asap via Phone of SNCF (French Rail) but i doubt there are still free seats :/

Plan B. take a TGV till Perpignan and catch from there regionaltrains via Portbou/Cerbere to Barcelona :)

 

Alternatively, you can leave Paris with the 7:11 TGV, arrive in Perpignan at 12:12 (20€ seats stil available):

No reservations needed from Perpignan.

Thank you guys, ahhh I feel like a real novice now with this! haha. Would there be a better alternative route to get us to Lisbon? Or anything else you would recommend. We have Eurostar booked for Monday 6th June and need to be in Lisbon for the evening of Thursday 9th. 
I just thought it was a hop on hop off kind of scenario! 🥺

I’m also just getting this then I'm trying to search your suggestions and the times of 07:11 don’t come up?

The 8:12 train from Paris is fully booked, according to SNCF.

The 7:11 train still has seats left.

Please don't use either the rail planner app or the booking website to plan. Neither are updated frequently enough.

The 7:11 train exists, e.g. check French railways.

For Lisbon, check seat61.

You could think about going via Hendaye, which is shorter anyway.

Thanks rvdborgt, which website would you use to look and can you use the interrail pass on the other websites to book?

For timetables in Spain, www.raileurope.com is a good one. Currently, also the DB website includes Spain (and Portugal). Do note though that it won't find connections via Hendaye since the only trains between Hendaye and Irún are Euskotren, which is not in any planner except for their own one (Interrail is not valid but they're cheap). So you need to search to Hendaye and from Irún.

In principle, you can book reservations anywhere you like. In practice, for Spain, choices are quite limited.

See this post for booking domestic Spanish trains.

See this post for booking TGV/AVE between France and Spain.

Portuguese reservations can only be booked in Portugal.

And the leg Mad→ Lis is one of the worst (except in Balkans) rail connection between 2 capitals in neighbor countries- 3 trains needed without even possible to book the mandatory REServ in train #3-the middle leg is a tiny dieselset chugging the distance over the border.

Frankly-unless you are married with trains: check bustimes, flix or alsabus.es (= Nat. Express in fact), they also run overnite-and if yes, check how to get to Estaci del Sur de Autobuses in Mad (metro)

Thank you all so much! We’ve actually decided to fly to Porto, and then enjoy the rail down to Lisbon at a more leisurely pace. I think we were a little naive on how easy it would be, but we did get the 50 year anniversary 3 month pass for £380!!! so I'm sure we will make that worthwhile over the summer for sure. Thank you again so much