The 18-year-old, who plays his club football with Quito, is currently on international duty at the South American Youth Championship in Argentina.
"I am very happy and very proud that after weeks and months of negotiations, the transfer has gone through," Goal.com quotes Cevallos as saying.
"I have already signed the contract. As soon as the tournament ends, I will go straight to Turin. I'll fight to earn my place and I am certain with God's grace it will go well."
Spanish side Villarreal were also thought to be interested in Cevallos.