Ambrose, the 2003 and 2004 V8 champion, will team up with Dick Johnson Racing for 2015, in partnership with American motorsport great Roger Penske.
The outfit will be known as DJR Team Penske, and will race Ford Falcons.
But his old foes are already writing him off.
Tasmanian Ambrose won 15 V8 Supercars rounds between 2001 and 2005. Photo: Getty
Long-time foe Greg Murphy said Ambrose, now 38, would find his V8 return tricky.
“I definitely know this sport isn’t what it used to be,” Murphy told News Corp.
"I think it will be a difficult thing for him to do after what he has done for the last nine years.
"We might not be mates or get along but I have to say he has nothing to prove. I have to have respect for what he has achieved in America.
“I think it will be difficult for him to find a place to do what he was doing when he left. It has changed a lot. He needs everything to go right.”
Should Ambrose return to the front of the grid in Australia, it would breathe new life into a category dominated by Red Bull Racing.
No.1 driver Jamie Whincup extended his series lead to 273 points at the Sandown 500 at the weekend, continuing what has been a predictable 2014 championship.
His team-mate Craig Lowndes is in second place, with Holden teams making up five of the top six on the leaderboard.
Veteran Holden Racing Team pilot Garth Tander joined Murphy in suggesting Ambrose would be shocked by the competitiveness of V8 Supercars.
“I know he drives on a few road courses but hasn’t he been doing a lot of only turning the car right?”
"I think the game's moved on a fair bit."
The Tasmanian announced last week he was returning home, bringing an end to his career in the American NASCAR series.
His venture with Dick Johnson Racing was confirmed on Monday.
"I just want to get my kids home to enjoy the Australian lifestyle so they can make a good choice when they grow up," Ambrose said.
"This is really a racing choice for me and I feel like the time is right for me to stop in the US."
In 2006, Ambrose relocated to the US to pursue big-money racing in NASCAR, starting with development category the Camping World Truck Series.
He moved up to the Nationwide Series in 2007, and later the Sprint Cup Series in 2008.
In 2011, he earned his first Cup Series win at Watkins Glen International, becoming the first Aussie to win in the highest level of NASCAR, and repeated that win the following year.
Penske runs the IndyCar team which won this year's IndyCar championship with Australian Will Power.
"We believe in building our businesses through racing and our success on the track," Penske said.
"With our new business ventures in Australia, it makes sense to showcase our brands through the V8 Supercars Championship and the opportunity to work with DJR and Marcos Ambrose convinced us to go forward."