It was a nervy night at the Parc des Princes for Carlo Ancelotti's side but a 1-1 draw against Valencia was enough to take them through 3-2 on aggregate.
PSG are in the running for three trophies this season - they are also in the quarter-finals of the Coupe de France - but their league title bid was dealt a blow last weekend with a shock 1-0 defeat by Reims.
They remain top of the table but are only two points clear of Lyon, meaning the pressure is on for Saturday's home match against struggling Nancy.
Midfielder Blaise Matuidi said on Wednesday night: "It's a great moment for us. We're in the running in three competitions - there aren't many sides in Europe who are in the same situation.
"We'll fight to go as far as possible in each one. It's historic. We pulled off something amazing, we shouldn't be scared of saying so. And we don't feel like stopping here, we want to go much further."
Striker Zlatan Ibrahimovic, suspended in Europe, will be available while David Beckham will hope to make his first Ligue 1 start.
The big game in Ligue 1 this weekend comes on Sunday, when Lyon meet third-placed Marseille, who are three points adrift of Les Gones.
Marseille were boosted by last weekend's results, when they were the only winners out of the top three, but striker Andre-Pierre Gignac knows defeat at Stade Gerland would be a major setback.
He said on Marseille's website: "Last weekend, it was the best outcome, but it can be a big blow against Lyon. We're going there to get a good result and get back the points.
"If we take the three points, we'll come back strong. PSG looked over the line but then they lost to Reims. Anything is possible."
Lyon drew with Brest last weekend and defender Samuel Umtiti admits they have been starting games too slowly.
He said on Lyon's website: "We must focus on our game, we must not relax. This year, when we produced our game, no team was a concern. In recent games we have gone missing in the first half, but we will not relax this time.
"It is too early to talk about the standings, there are still a lot of games. Nothing will be decided for second place."
St Etienne are hot on the heels of Marseille after six wins and two draws in 2013, while they have the Coupe de la Ligue final against Rennes to look forward to next month and a Coupe de France quarter-final.
Rennes are their opponents in Ligue 1 on Friday night, and victory in Brittany would lift Les Verts above Marseille, for 48 hours at least.
Winger Romain Hamouma said on the Ligue 1 website: "The squad is full of confidence and putting together very good results. We've got common objectives and, as long as we stay humble, we are capable of achieving beautiful things."
Another notable match at the top of the table on Sunday sees fifth-placed Nice host Montpellier in sixth. It will be the first match for Montpellier boss Rene Girard since he learned he will not be offered a new contract at the end of the season.
On Saturday, seventh-placed Lille visit Valenciennes, Reims will aim to follow up their victory over PSG when they meet bottom side Troyes, Ajaccio host Lorient, Brest meet Toulouse and Sochaux travel to Evian.
The other match on Sunday sees Bordeaux try to end a four-match losing run in the league against Bastia.