Ndiaye arrived in the summer from Olympique Marseille and has been a bright spot in a disappointing season so far for the Toffees.
He told the club's website: "I am very pleased. Obviously, I've come back to the Premier League, which I love, with a big club in Everton Football Club. I'm very grateful for the opportunity they've given me, and I want to give back.
"I will give my all to the Club, for the fans. Obviously, it's good to have a good connection with the fans - I've tried to give them something on the pitch and they've given me love outside the pitch. I'm very happy here."
On last week's defeat at Southampton, Ndiaye added: "We had a disappointing start to the season but we provided a reaction with a five-game unbeaten run - and now we need to show another strong reaction as we look ahead to the weekend. We will give it our all, that's for sure."