Parling played for the Rebels in 2018 and has made successful transition into coaching, engineering the Melbourne lineout over the past two years.
In Super Rugby AU, the Rebels had the best lineout success (88 per cent), ahead of the Brumbies and Waratahs (both 83 per cent).
Brumbies coach McKellar was the first target for the Wallabies, but told Dave Rennie he wanted to remain working in Canberra this year after his assistant Peter Hewat opted to take up a role in Japan.
Parling, 36, will join new Wallabies scrum coach Petrus du Plessis, attack coach Scott Wisemantel and defence coach Matt Taylor, with the Wallabies squad set to assemble next week for the first time this year.
Melbourne’s strength and conditioning coach coach Shane Lehane and physio Dan Mannix will also join the party.
Playing 29 tests for England and with a Lions series win in 2013, Parling said he was honoured to be joining the Wallabies set-up.
“I’ve really enjoyed helping develop the players we’ve had in Melbourne, so to now get the opportunity to join Dave’s coaching team for this test season is a real honour,” Parling said.
Rennie said he was lucky that Parling was available at short notice, with an advantage being his knowledge of current players.
“He’s technically very strong around lineout and maul and he has impressed me with his work ethic to get up to speed over the last two weeks,” Rennie said.
“There have been a lot of challenges so far in 2020 and we’ve had to be agile and adaptable, none more so than Geoff who has already made so many sacrifices while being on the road with Rebels this season but he still jumped at the opportunity to join our team.”
Parling will return to Melbourne following the Wallabies 2020 test season, ahead of the Rebels 2021 Super Rugby season.