"I'm an ambitious person and this represents a great opportunity for me to develop as a player," the defender told reporters on his official presentation.
"I always look at the present and future. I don't consider myself a traitor because I've always underlined the fact that we're professionals.
"I've received more advice than criticism over the past few days."
Ogbonna helped Torino to climb out of Serie B in 2011-12 and establish themselves in the top flight last season.
Born in Italy to Nigerian parents, the 25-year-old has won six caps for Italy and was included in the squad for Euro 2012.
Juventus said he was the 11th player to make the move from Torino.
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