The versatile prop, who can play both tight-head and loose-head, has a wealth of top flight experience, having played in both the Heineken Cup and Top 14.
London Wasps chief executive Chris Thomas said: "We are making no secret of the fact that we want to strengthen our pack in time for next season and this is the first of a number of signings we hope to make in this area. Jeremy's versatility in the front row will be a real asset to the squad."
Jeremy Castex said: "I am really excited to be joining such a fantastic club. It will be a great challenge and I am looking forward to working with some great forwards like Simon Shaw, Joe Worsley and others and being coached by a World Cup winning prop in Trevor Woodman."
Castex is the fourth player to be signed by the club in recent weeks following announcements that backs Nicky Robinson (from Gloucester), Ryan Davis (from Exeter) and Chris Bell (from Sale) will also join London Wasps next season.