Tevez, 31, started his career at Boca before leaving in 2004 and returns to Argentina after nine years in Europe.
Former Manchester United, Manchester City and West Ham forward Tevez struck 20 Serie A goals last season and had been linked with Liverpool, Atletico Madrid and Paris St-Germain.
Juventus had already replaced Tevez with Mario Mandzukic from Atletico.
Boca Juniors confirmed the transfer while Tevez was on the bench for the Copa America quarter-final against Colombia.
Shortly after the announcement was made, Tevez came on to score the winning penalty in a shootout to send Argentina into the last four.
Boca president Daniel Angelici said: "It is a day of joy and great satisfaction. The return of Carlos Tevez in an extraordinary moment of his career is fantastic news for all partners and supporters of Boca and Argentine football. The presence of Carlos will give another leap in quality to the great squad we have."
Tevez, who has won three league titles in England and two in Italy, scored 38 goals in 110 games during his first spell at Boca, where he won the league in 2003 and was voted South American Player of the Year for three straight seasons.
He left for Brazilian side Corinthians before the 2005 season, and moved to West Ham the following year.
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Argentina striker Carlos Tevez has completed his move back to Boca Juniors from Italian champions Juventus.