The former Formula 1 racer is no stranger to the V8-powered S5000 series, having contested the two-round Tasman Series in 2021.
That cameo included a race win at Sydney Motorsport Park.
Merhi is now set to make his debut in the Australian Drivers' Championship when he joins Garry Rogers Motorsport for the opening round at Symmons Plains on February 24-26.
He'll join Nic Carroll, Jordan Boys and Aaron Cameron in the GRM line-up.
"I am very happy to come back to S5000 together with GRM," Merhi said.
"I have very nice memories from my time there. Last time I was in Australia was 2021 and I was pretty close to winning the Tasman Series.
"I am looking forward to jumping in the car again and it will also be a new track for me, which is always challenging.
"I will try to do my best and adapt quickly to the car and the circuit again."
