The 20-year-old will team up with Stevens-Miller Racing for a maiden full assault on the US series.
He will be split his time between Indiana, where SMR is based, and Michigan, home of Howe Racing Enterprises, the constructor of the chassis he will race this season.
The deal follows a sensational one-off outing for SMR in the American Trans Am Series at the end of last year, where Herne finished a fine fourth at the Circuit of the Americas.
In recent years Herne has built a reputation as one of the top young drivers in Australia.
He won two Australian Trans Am titles on the bounce in 2021 and 2022 with Garry Rogers Motorsport, as well as the S5000 Tasman Series this year.
However a move into the Supercars system has proved elusive for Herne, largely due to a lack of a budget.
Having not been able to afford to race in the second-tier Super2 series since means he is still technically ineligible to race in Supercars.
Instead he could now be on the path to NASCAR, Herne highlighting Trans Am's growing stature in the US racing pyramid ahead of his move.
“It doesn’t feel real to be honest, I don’t know how to feel right now," said Herne.
"[SMR owner] Joe Stevens and Howe Racing are really putting all their eggs in my basket to try and win the 2023 title, so it’s daunting, but also pretty cool.
“They want to get the championship. It is very competitive over there, and there are a bunch of NASCAR teams now putting their junior drivers and main game drivers in the category to groom them for NASCAR.
"NASCAR is going more towards the road course route and TA2 over there is the biggest road racing series they have, so it’s a bit of a pinch yourself moment to think I’ll be in the category in just under two months time.
“I’ve had a taste of the racing and the class at COTA, and it was very eye-opening. It was the first time in my racing career that I’d thought, 'gee, I could be out of my depth a bit here,' but I went well in my first race.
"I proved that I was one of the fastest drivers there, and I want to put in a good fight for the championship.
“I don’t want to set any expectations. I know I’m going to give it everything I have, and if worse comes to worse, I’ll come back to Australia with a year's bucket list ticked off. But best case, I stay in the States and build on a great year and make the most of the opportunity."
GRM boss Barry Rogers, who has been instrumental in Herne's career to this point, backed the young gun's Stateside move.
“We are tremendously proud of what Nathan has achieved during his time with GRM which all began back in 2020 when we tested him in a Supercar,” said Rogers.
“Nathan had just turned 18 years old, and [team owner] Garry [Rogers] was so impressed with Nathan that it motivated him to enter a Bathurst wildcard.
“Unfortunately, Nathan was not given an exemption for a Superlicence although only one point short of automatically qualifying for one, and the opportunity to race at Bathurst was gone.
"Subsequent rule changes to the Superlicence system that required drivers to compete in Super2 saw Nathan’s opportunity to race at Bathurst dissipate as the funding for such a programme was not available.
“Nathan put his head down and bum up and showed immediately his driving talents in Australia’s fastest race cars, the S5000s, and dominated the past two Trans Am seasons.
"We are so happy that Nathan has been given an opportunity in the US and it illustrates to young drivers there are many opportunities out there for those who have the talent and not necessarily the budget."
The 2023 American Trans Am season kicks off at Sebring International Raceway on February 23-26.
