Ogbonna, who combines an impressive physical presence with a cultured left foot, was raised at Torino, helping them to secure promotion from 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.
Ogbonna, who escaped almost unharmed from a car crash in 2008 when his vehicle went off a bridge and ended up in a river, faces a battle to win a place in the first team.
Last season Juventus boasted the strongest defence in the league, conceding only 24 goals in the 38-match campaign.
He is Juve's third big close-season signing after forwards Carlos Tevez and Fernando Llorente joined the club.
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