Grey was the Wallabies defence coach under Michael Cheika at this year's World Cup in Japan but, with Cheika replaced by Kiwi Rennie, will move into a new role in 2020.

Larkham, a former Wallabies attack coach, briefly held the job this year before moving on to work with Irish giant Munster.

Grey's duties will be expanded, however, with the 44-year-old also serving as technical director of the Sunwolves for next year's Super Rugby season.

The appointment opens the door for former Waratahs team manager and Sunwolves adviser Chris Webb to return to Australia as the Wallabies team manager.

Wallabies World Cup attack coach Shaun Berne has already returned to his full-time role with Melbourne Rebels, with England's attack coach Scott Wisemantel to join Rennie's staff.

According to Rugby Australia, the Grey move is designed to strengthen their relationship with the Japan Rugby Football Union (JRFU).

"Grey's secondment will focus on providing technical advice and coaching to the Tokyo-based Super Rugby side in support of new Sunwolves head coach Naoya Okubo," RA said in a statement on Monday.

Grey will also oversee the Sevens teams, who will play in the Tokyo Olympics next year, the Wallaroos, Junior Wallabies, and elite junior programs.

"I've enjoyed my time as an assistant at both the NSW Waratahs and the Wallabies for the last four years but this is now an opportunity for me to continue my development as a coach," Grey said.

"The Sunwolves have an incredibly talented group of players that are keen to learn, and the same can be said of the coaching staff in Tokyo too.

"We all saw from the recent World Cup just how much ability and potential there is in Japan, and I will be doing all I can to help in their development."

RA director of rugby Scott Johnson said the new role was a way to keep Grey in the system, which has identified a dearth of young Australian coaches.

"Nathan has proven himself to be a great young coach and he's one that we didn't want to lose out of the system," Johnson said.

"We want to see him continue to grow and evolve and that will happen now with Nathan to be given a bit more responsibility and scope."

Australian Associated Press