Upvote:6
As stated in comments, going to Saint Jean Pied du Port from Barcelona can take quite long. Unless necessary to go via Barcelona, try to get a flight to Bilbao or San Sebastián, so that you can decrease the travelling time. You can even check flights from Barcelona to Bilbao, which can be found for good prices.
Anyway, if you decide to go from Barcelona, you should take these steps:
Get a bus from Barcelona to Pamplona.
In Pamplona, get a bus straight to Saint Jean de Pied de Port