Gardner, the son of 1987 500cc champion Wayne, has been a fixture on the Moto2 grid since 2016 and has enjoyed improved fortunes since joining the SAG outfit last year.
The Australian is currently in the middle of his best season in the category, with a pole position and a podium at the Red Bull Ring placing him 11th in the standings with eight rounds still to run.
following Johann Zarco’s dismissal from the outfit, will join the Austrian marque’s affiliated Moto2 team Ajo in 2021.
"I am very happy to be signing this contract for the team of my dreams,” said Gardner. “I am proud to be part of the Red Bull and KTM family, and of Aki [Ajo]’s structure. I want to thank all of them for giving me this opportunity for 2021.
“I also thank all those who have helped me to get here. I can't wait to start working with them next year and I hope that together we can do some amazing things."
Ajo, which switched to Kalex bikes this year following KTM’s withdrawal from Moto2 as a manufacturer, is fielding Jorge Martin and Tetsuta Nagashima in 2020.
Gardner will likely take the seat vacated by Martin, who is expected to step up to MotoGP to replace Ducati-bound Jack Miller at Pramac.
“I'm very happy to have Remy in our project next year,” team principal Aki Ajo said. “He is a young talent, but at the same time he has extensive experience in the FIM World Championship.
“This combination of abilities is perfect for our project of developing riders. We are looking forward to working together next season. I know that Remy has something special compared to the rest of the competitors: he has great talent, a good feel for the bike and is a born fighter.
“I hope that, as a team, we can give him a boost during the season for the style that comes naturally to him. I am personally very excited to have Remy with us, and about what 2021 has in store."
In Moto3, Darryn Binder, brother of KTM MotoGP rider Brad, will switch to the Petronas Sprinta team in 2021, marking a switch from KTM to Honda machinery.
Tech 3, meanwhile, has elected to retain both Deniz Oncu and Ayumu Sasaki for the next season in the lightweight class.