Cheika has answered RA's SOS call to return some 13 years after guiding the perennial under-achievers to their one and only Super Rugby crown.
The 59-year-old has agreed to a two-season deal after ending a successful stint as a Sydney Roosters' NRL assistant coach.
"The NSW Waratahs have always occupied a special place for me - it's my home state and I feel ready to return as their head coach ahead of an important year for the Waratahs and also for Australian rugby in the lead up to the home Rugby World Cup (in 2027)," Cheika said.
Also the first coach to pilot sides to major titles in the northern and southern hemispheres after leading Leinster to 2009 European Cup glory, Cheika has been commissioned to arrest the Waratahs' alarming decline.
One of Australia's biggest, oldest and proudest clubs, the RA-run Waratahs have missed the past three Super Rugby Pacific finals despite boasting a Wallabies-laden roster.
"He's a proven winner and (has) a really good track record of success," Tahs high-performance manager BJ Mather said on Wednesday.
"We don't want to hark back to 2014 all the time, but you know he's the last Waratahs head coach to have won the Super Rugby Comp, so he sees an opportunity here to try and build something again to make the Waratahs successful."
Dan McKellar was let go with a year remaining on his contract following two frustrating seasons in charge, after taking over from Darren Coleman at the end of 2024.
Mather expects Cheika to be chasing immediate success.
"He's got a good track record of that, hasn't he? He usually gets a good bounce when he comes into a club," he said.
"So 'Cheik'' probably backs himself to get that performance bounce in the very near future ... for the Waratahs and for Australian rugby as a whole, we need to be successful."
Cheika, who coached the Wallabies to their most recent Rugby World Cup final in 2015, will reunite with his 2014 premiership-winning halves Bernard Foley and Nic Phipps, who were announced last week as marquee signings.
World Rugby's 2015 coach of the year will also have superstars Joseph Aukuso-Suaalii and Max Jorgensen and Roosters recruit Angus Crighton in his Waratahs backline next season.
But Mather said Cheika could still splash out on more big names if he feels the need.
"We can always have a good go. If there's a target out there that we think fits the way that he wants to play, and is available to us, we'll have a good crack at that," Mather said when asked how much room there was left in the Waratahs' salary cap.
"We want to get better, we need to win games. We know that and whatever we need to do to be successful, we'll do the best that we can."
Cheika made a hasty and acrimonious departure after the Wallabies' quarter-final exit from the 2019 World Cup in Japan.
"They say time heals all wounds," Mather said.
"It's a long time ago when he he left and there's a lot of water under the bridge.
"So when his name came up in conversations there were never any major obstacles raised as a red flag not to have that conversation and see if he was interested - and vice versa."
Cheika will officially start back at the Waratahs in November after coaching Lebanon at the Rugby League World Cup.
