Five-time winners Toulouse are the most successful club in the history of the Champions Cup and booked their place in the last four as they saw off a spirited Exeter side in the quarter-finals.
Willis has won 14 England caps but is ineligible for Test selection because of a Rugby Football Union (RFU) rule that means players can only be picked for the national team if they compete in the Premiership.
The flanker, however, is relishing playing alongside stars such as France internationals Antoine Dupont and Romain Ntamack, and Scotland’s Blair Kinghorn.
He added: “When I first came I only signed for a few months and then I made the decision to extend with good reason.
“It’s an incredible place with a great group of players, coaches, and people around the club.
“It’s so competitive and it really tests you as a player. When everyone is fit you have to be at your absolute best to be picked and I love that.”
Willis says the club’s European pedigree is also not lost on him.
“When it comes to Europe, it is incredibly special,” said Willis. “We have such a rich history in the competition and they are so passionate to add to that.
“The president pushes the coaching staff and the coaching staff push us and we all want to win things. This group has the belief but we know how much hard work that means.”