Cox, an internet sensation thanks to his exploits in production car racing, made his TCR debut last time out at The Bend in a third Wall Racing Honda, running near the front all weekend and finishing fourth in the final race.
He's now set for a second start in the series in Ipswich next weekend, however this time he'll replace Jimmy Vernon in the GRM Alfa Romeo.
“We have been watching Jordan for several years and he is very impressive in a front-wheel-drive car," said GRM boss Barry Rogers.
"Like many he came to our attention following the on board vision across the top of Mt Panorama and a couple of years ago we watched him in his Honda Civic at the Adelaide 500 where again he showed immense ability in a front-wheel-drive car.
“We obviously have several cars on the horizon for 2020 and there will be drives available, so it’s a good opportunity to assess possible candidates. For us, a driver’s ability is very important, but even more so is how they integrate with the team and their work ethic and attitude."
Cox added: “It’s an outstanding opportunity. It’s the biggest chance I’ve ever had in motorsport and one that I’ve very grateful for.
“It’s a bit of mixed feelings. We were making progress with Wall Racing, they are great guys, but Garry put an awesome deal on the table and its one that I have to take."
The deal is currently a one-off, with Vernon set to return for Round 5 at Winton later next month.
"Jimmy is a young man with plenty on his plate including the responsibilities of running the families sign writing business," added Rogers.
“After getting involved in a few incidents, we felt it best to give him a round on the sidelines to take breath and really think about how he goes about his racing and how much he really wants to do it.
“We expect that the break will do Jimmy the world of good and he’ll be back behind the wheel at Winton for Round 5.”