La Rochelle reached the French Top 14 final for the first time on Friday with a 19-6 victory over Racing 92.
They will face either Toulouse or Bordeaux-Begles, who meet on Saturday, in the title match.
Toulouse defeated La Rochelle 22-17 in the European Champions Cup final last month.
Friday's win was a landmark achievement for La Rochelle who were only promoted to the top flight seven years ago.
Twice before they had fallen at the semi-final stage -- against Toulon (18-15) in 2017 and Toulouse (20-6) in 2019.
For Racing, it was a third loss in four years at the last-four hurdle.
In 2017 and 2018 they were defeated by the eventual champions Clermont (37-31) and Castres (19-14).
On Friday, in front of 5,000 spectators inside the football stadium of Ligue 1 champions Lille, La Rochelle shrugged off the injury absences of Pierre Bourgarit, the suspended Levani Botia as well as Jeremy Sinzelle, Pierre Aguillon and Geoffrey Doumayrou.
La Rochelle's New Zealand coach Jono Gibbes, who will replace Franck Azema at Clermont next season, had no hesitation in pairing South African Raymond Rhule and Jules Favre at centre.
That was despite the intimidating presence of Virimi Vakatama and Gael Fickou on the other side.
The match was also a contrast in styles with the La Rochelle forwards, boasting the best defence in the championship, putting their reputation on the line against a Racing team scoring points for fun since the arrival of Fickou mid-season.
However, Racing looked weary having had to see out a first round play-off last week with a 38-21 win over Paris rivals Stade Francais.
La Rochelle, by contrast, had enjoyed a two-week break having finished the regular season in second place and going straight to the semi-finals.
They scored the game's only try on the half-hour mark with winger Arthur Retiere crossing after linking up with full-back Brice Dulin.
New Zealand fly-half Ihaia West kicked five of six goals while Racing's points came from two first-half penalties from Maxime Machenaud.