Di Giannantonio began his Grand Prix career in 2015 when he was called up by Gresini Racing as a wild-card replacement for the injured Andrea Locatelli at the Valencian Moto3 round. Simultaneously that year he finished runner-up in the Red Bull MotoGP Rookies Cup and in the CIV Moto3 championship. He joined Gresini full-time for 2016 and scored his first points and first podium — second place — at Mugello, following it with further podiums at Assen and Brno.
He remained with the Del Conca Gresini Moto3 squad in 2017 and 2018. The 2018 season was his strongest in the small class: four podiums and two race victories helped the team win the Moto3 Teams' Championship alongside teammate Jorge Martín.
Di Giannantonio moved to Moto2 with Speed Up Racing in 2019. He collected two podiums — at Brno and Misano — in an otherwise unspectacular debut year, then matched that tally with two more podiums in 2020.
A switch to Federal Oil Gresini Moto2 for 2021 lifted his results noticeably: three podiums and a race victory placed him seventh in the championship standings, comfortably his best intermediate-class season.
Di Giannantonio joined the Gresini Racing MotoGP team on a Ducati Desmosedici for 2022. His debut premier-class campaign was largely a learning exercise, with a best result of eighth at the German Grand Prix and twentieth in the standings. One notable moment was his first pole position in the class at Mugello. In 2023 results improved across the board: seven top-ten finishes, two podiums, and — crucially — a maiden MotoGP victory.
In October 2023 Marc Márquez announced he would join Gresini for 2024, ending Di Giannantonio's seat. Rather than triggering a crisis, the announcement seemed to galvanise him: he immediately responded with his first premier-class podium at Phillip Island and then won the season-closing Qatar Grand Prix, finishing twelfth overall and securing himself a MotoGP ride for 2024.
Di Giannantonio moved to the VR46 Racing Team — the satellite Ducati squad founded and owned by Valentino Rossi — for 2024. He delivered his most consistent MotoGP season to date: only one result outside the top ten across the full year. Without a race win he nonetheless finished tenth in the championship, his highest career standing. He was rewarded with a two-year contract extension covering 2025 and 2026, and for 2025 VR46 secured factory-specification Ducati equipment for their riders.
The 2025 season showed further growth. He opened with a podium finish at the Grand Prix of the Americas and later claimed his first home podium at the Italian Grand Prix at Mugello, overtaking factory Ducati rider Francesco Bagnaia on the penultimate lap for third place.
Di Giannantonio is known for aggressive racecraft and strong performances at high-speed circuits. His ability to extract pace from Ducati machinery — even when running satellite-spec bikes against factory opposition — established him as a valued development asset within the Ducati structure. The late-2023 surge at Phillip Island and Qatar, produced under the pressure of losing his seat, is considered one of the more remarkable form reversals of his generation.