Aina has joined on a season-long loan with the option to sign permanently.
“Torino had been tracking me for some time and I hope to do well here," the 21-year-old said on the official club website.
“I know this is a club that believes in young players and that is very important. I know I can learn so much in Italy, above all in terms of positioning, tactics and organisation, as those are fundamental here.
“I really want to experience this new adventure to the full. Thank you to Toro for having chosen me: now it's up to me and I can't wait to get started."
President Urbano Cairo also presented new signing Aina to the supporters.
“We were seeking a prospect like Ola Aina, a wing-back who is physically strong, quick and has stamina, able to work on either flank.
“Aina is an ambitious young player who Torino can further improve. In name of the club, I am happy to welcome him to the Granata."