Pivac and Patchell previously worked together at Scarlets and Japan club NEC Green Rockets Tokatsu.
“I’m pleased to reconnect with Rhys after coaching him at the Scarlets and with the Welsh national team,” said Pivac.
“The last time we worked together was in Japan, where Rhys took on a player-coach role, focusing on attack and mentoring younger players.
“He had an outstanding playing career, leading the attack wearing the number 10 jersey.
“We share the same vision of the game. We want to play a style that excites both players and fans.”
Benetton president Antonio Pavanello stated Patchell’s appointment was at the top of Pivac’s wish list.
“Wayne made specific requests, only a few, but very precise,” said Pavanello.
“Among these was the choice of Patchell, which we carefully evaluated and decided to support, convinced he is the right fit for our path.
“We are confident he can make a significant contribution to the team’s development and that his work will translate into tangible results on the field.”