Folger will work with incumbents Dani Pedrosa and Mika Kallio on the 2023-spec KTM RC16 in his new role, joining the team just before the start of official testing at the Sepang International Circuit in Malaysia on February 5-7.
His appointment comes as KTM aims to mount a serious challenge for the title this year, having finished fourth out of six in last year’s manufacturers' championship.
The Austrian marque has also changed its factory line-up for 2023, with Jack Miller joining, replacing RNF-bound Miguel Oliveira and partnering Brad Binder.
“As the MotoGP season comes closer then the schedule for our test team also comes to life,” said KTM MotoGP director Pit Bierer.
“Not many people see the crucial work these guys are making towards our project but their contribution is essential.
“For that reason, we have chosen to add Jonas to the team alongside Mika and Dani; who have both already built-up so much knowledge of our race bike and the steps we have made.
“We know Jonas quite well and he’s briefly ridden our bike before. He knows what it takes to put a motorcycle at the front of a Grand Prix and he is still young and has a lot to contribute. Compared to Dani and Mika he has a different body-type and style and that will also help us with our development.
“The test team is a fantastic group and I cannot stress enough how much of a strong foundation it makes for our MotoGP racing.”
A three-time race winner in the Moto2 ranks between 2015 and 2016, Folger made his MotoGP debut with Tech 3 Yamaha in 2017 and claimed second on his home turf in Germany, but his rookie campaign was cut short after he was diagnosed with Gilbert’s syndrome.
After spending some time on the sidelines, he was tasked with spearheading Yamaha’s European test team in 2019, gaining experience of managing the testing programme of a factory.
When the Japanese manufacturer elected not to renew his contract at the end of the 2019 season, Folger moved outside of grand prix racing, winning Germany's IDM championship the following year on a Yamaha R1.
This helped him land a full-time seat in the World Superbike Championship with Bonovo BMW in 2021, but Folger struggled to acclimatise himself to the M1000RR after a career spent almost entirely on Yamaha machinery, and he could muster a best finish of eighth before his team elected to sit out the final rounds of the season.
His deal with KTM means he will be back in the MotoGP paddock for the first time in six years.
