A late Ihaia West try ended Racing 92's stiff resistance as La Rochelle booked their place in a second successive Champions Cup final.
Ronan O'Gara's side, who were beaten by Toulouse in their debut Champions Cup final at Twickenham last season, will face Leinster in Marseille on 28 May.
Hosts Racing had to relocate the game to Lens as their La Defense Arena in Paris was being used for a music concert.
LENS, FRANCE - MAY 15: Ihaia West of La Rochelle, passes the ball during the Heineken Champions Cup Semi Final match between Racing 92 and La Rochelle at Stade Bollaert-Delelis on May 15, 202...