Gardner made his first three Grand Prix appearances in the Moto3 World Championship in 2014, competing twice as a replacement for injured riders and once as a wildcard entry, scoring one point in Malaysia. In 2015 he was given a full-time seat with the Mahindra-equipped CIP team, achieving his best result of 10th place at his home race at Phillip Island.
Gardner transitioned to the Moto2 World Championship in 2016 with Tasca Racing's Kalex as a mid-season substitute for Alessandro Tonucci, scoring eight points and earning a full-time ride for 2017. Two seasons with Tech 3 Racing followed, marked by crashes and a training injury in 2018 that cost him part of the season, though he showed promise with a fifth-place finish at Valencia that year.
For 2019, Gardner joined the SAG Team alongside Tetsuta Nagashima. He scored his first Moto2 podium with second place in Argentina and finished 15th in the standings with 77 points. His trajectory continued upward in 2020 — collecting three podiums including second in France and third in Austria — before winning the final race of the season in Portugal, his first Moto2 victory. That result was enough to displace Nagashima at Red Bull KTM Ajo for the following season.
Gardner's 2021 campaign with Red Bull KTM Ajo was dominant. Paired with Raul Fernandez, the two riders monopolized the season, together winning 13 of the 18 races held. Gardner contributed five victories, six second-place finishes, and a third place, never finishing outside the top ten except for a single crash in the United States. The championship was decided at the final race in Valencia, where Gardner's 10th-place finish was enough to secure the title with 311 points — four ahead of his teammate Fernandez.
Both Gardner and Fernandez were promoted to MotoGP in 2022 with KTM's Tech3 satellite team. The season proved difficult, and in September 2022 Gardner was told he was being released at the end of the year, reportedly for reasons of professionalism despite outperforming his teammate in the standings at that point.
Gardner was unable to secure a full-time MotoGP seat for 2023 and instead joined Yamaha for the Superbike World Championship with the GRT Yamaha WorldSBK Team. He briefly returned to MotoGP in 2024 as a replacement for the injured Alex Rins with the Monster Energy Yamaha MotoGP Team, competing at the German, British, and Japanese Grands Prix as a wildcard without scoring points.
As the son of Wayne Gardner, Remy carries one of Australian motorsport's most storied family names. His 2021 Moto2 title validated a career that had to overcome significant setbacks, injuries, and team changes across seven seasons in the intermediate class. The father-and-son combination of a 500cc world champion and a Moto2 world champion stands as a unique achievement in Grand Prix motorcycle racing.