Juve defender Mattia Caldara will also move to Milan as part of the complex three-way deal, the clubs said on Thursday.
Higuain, 30, will join Milan on a one-season loan for 18 million euros (16.03 million pounds) with an option to buy at the end of that period, the two Italian giants added.
Juve have bought Bonucci for 35 million euros ,one year after selling him to Milan, who have signed Caldara for the same amount in what is effectively a swap. Both players have signed five-year contracts.
Higuain moved to Juventus in 2016 for 90 million euros after scoring a record 36 Serie A goals in the previous season for Napoli and his sudden departure infuriated that team's supporters.
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The 30-year-old has won Serie A and Coppa Italia titles in each of his two seasons with Juve and netted 55 goals in 105 appearances in all competitions, including 40 in 73 Serie A outings.
Critics, however, say he has failed to make an impact on the big occasion.
He had a subdued World Cup where he started one game, appeared as a substitute in two more and failed to score a goal. He was left on the bench for the second round match against France as Argentina lost 4-3 and were knocked out.
Higuain appeared to become surplus to requirements after Juventus signed World Player of the Year Cristiano Ronaldo last month.
'BBC' DEFENCE
Bonucci's return to Juve reunites him with Andrea Barzagli and Giorgio Chiellini, who together formed the so-called 'BBC' defence which was one of Europe's most formidable rearguards.
The 31-year-old, who has played 80 times for Italy, left the Turin club for 40 million euros one year ago amid reports that he had fallen out with coach Massimiliano Allegri.
Barzagli, 37, extended his contract for another season in June.
Juventus have won the last seven Serie A titles and their main ambition now is to win the Champions League, after finishing runners-up in 2015 and 2017.
Seven-times European champions Milan have had a series of disappointing seasons since they won their last Serie A title in 2011.
Caldara, 24, was signed by Juve from Atalanta in January 2017 but remained at the Bergamo club on loan until June. In all, he made 55 Serie A appearances for Atalanta, helping them qualify for last season's Europa League.
He never played a match for Juventus.
(Reporting by Silvia Recchimuzzi in Gdynia and Brian Homewood in Zurich; Editing by Toby Davis and Ken Ferris)
