Juve have paid €20m to Nice for the midfielder, who's father Lillian also played for the Bianconeri.
“I dreamed of joining Juventus since I was a child, so I am very emotional and happy at this special day,” Thuram told the official club website.
“I remember when my father played at the Stadio Delle Alpi, I remember Zlatan Ibrahimovic, that I lived here and thought my brother was the best in the world.
“My Dad talked about Juve as the biggest club in Italy, he sees it as the biggest club in the world, and when you arrive at Juventus, you must play to win.”
He also said: “The first contact with Juve was when I was playing at Monaco, at the age of 17. I’m happy the club came back looking for me. If Juve call, you can only say yes.
“I like to run with the ball, defend, but also attack. I love football, I enjoy being on the pitch with my teammates and winning.
“I salute the fans and hope to see them soon. Fino alla fine.”