Leading 3-2 from last week's first leg at home against their domestic rivals, Lyon went ahead early on in the return in the French capital with a Selma Bacha strike.
Tabitha Chawinga levelled for PSG on the day before half-time, but Haitian talent Melchie Dumornay fired in late on to win the game for Lyon and clinch the tie. Lyon will face Barcelona - who beat Chelsea 2-1 on aggregate in the other last-four tie - in the final in the Spanish city of Bilbao on May 25.
That ensures the trophy will again go to one of the two teams who have dominated the competition in recent seasons, sharing the last eight Champions Leagues between them.
Lyon won it six times in seven years before Barcelona reclaimed the trophy last season. Lyon have also twice beaten Barcelona in the final, winning 4-1 in Budapest in 2019 and 3-1 in Turin in 2022.
The French club's tally of eight Champions League victories is comfortably a record. No other team has won the title more than four times.
Lyon had seized the upper hand in the tie with a remarkable comeback in last week's first leg, recovering from 2-0 down at home to win 3-2 with three late goals in the space of seven minutes.
They built on that, and dampened PSG's hopes of turning the tie on its head again, by going in front just three minutes into the return in the sunshine at the Parc des Princes.
Bacha played a corner short from the right and then latched onto the return ball to lash a low shot on her left foot that fizzed past goalkeeper Constance Picaud and in at the near post. PSG were seeking revenge for defeats against Lyon at the same stage in 2020 and in 2022, as well as a loss on penalties in the final in 2017.
They were given hope shortly before half-time when Marie-Antoinette Katoto picked out Chawinga and the striker from Malawi fired a low strike into the far corner for her sixth goal in the competition this season.
The hosts then spent the second half chasing the game but Lyon made sure of their victory with nine minutes left when Amel Majri deftly laid the ball back for Dumornay to score.
Barcelona sealed their spot in the final on Saturday when they beat Chelsea 2-0 in London to overturn a 1-0 first-leg deficit. Reigning Ballon d'Or Aitana Bonmati levelled the scores on aggregate in the first half at Stamford Bridge.
Chelsea had Kadeisha Buchanan sent off just before the hour before Fridolina Rolfo's 75th-minute penalty won the tie for the defending champions.