Vietti began competing in Italian domestic motorcycle racing from a young age. In 2015, he won the Italian Premoto3 250 4t championship — a CIV category — claiming seven of eight races. On 15 December 2015, he joined the VR46 Academy. He progressed through the CIV Moto3 category in 2016 before moving to the CEV Junior World Championship with SKY Racing Team VR46 in 2017, finishing 25th. In 2018 he competed full-time in the FIM CEV Moto3 Junior World Championship, scoring a second place at Barcelona and finishing tenth overall with 52 points.
Vietti graduated to the Moto3 World Championship in 2018 as a mid-season replacement for Enea Bastianini in the Estrella Galicia team, initially stepping in for VR46 Academy member Nicolò Bulega at the Japanese Grand Prix. He marked his first appearance with a podium at Phillip Island the following week — a third place — and added a tenth place at Valencia before the season ended. Despite taking part in only a fraction of the season, he outscored Bulega by six points across 14 fewer races.
In the 2019 Moto3 World Championship, Vietti competed for a full season, with Bulega moving up to Moto2. He collected three third-place finishes — at Jerez, Barcelona, and Motegi — accumulated 135 points, finished sixth in the championship, and was awarded Moto3 Rookie of the Year. He began 2020 in similarly strong form and achieved his first Moto3 victory in Austria, followed by a second place at Misano and a second victory in France. He closed 2020 with two wins, four podiums, 146 points, and fifth in the final standings — his strongest Moto3 campaign — before graduating to Moto2.
Vietti joined Moto2 for 2021 under the Sky Racing Team VR46 banner, partnering Marco Bezzecchi. He improved progressively through the season, with his three strongest results clustered in the final three rounds: fourth at Misano, sixth at Portimão, and fourth at Valencia. He finished twelfth in the championship with 89 points, third among rookies behind Raúl Fernández and Ai Ogura. In 2022, partnered by Niccolò Antonelli under the Mooney VR46 Racing branding, Vietti continued to build experience in the intermediate class.
When the VR46 Moto2 programme was absorbed into the Fantic Racing structure for 2023, Vietti transitioned with the team and continued racing under the Fantic banner.
Vietti joined Red Bull KTM Ajo for 2024 and delivered three victories during the year — at the Red Bull Ring, at Misano, and in Malaysia — alongside an additional podium. The season was complicated by three collarbone fractures that forced him to miss multiple rounds. Despite the injuries, his wins reflected genuine pace when fit, and he finished seventh in the championship.
For 2025, Vietti joined Speed Up Racing alongside Alonso López, riding a Boscoscuro chassis — his first Moto2 season not on Kalex machinery. Adapting to the unfamiliar bike proved challenging. He took a podium (third) in Argentina and later in Austria at the Red Bull Ring. His sole victory of the year came at the Red Bull Grand Prix of Rimini and San Marino, a dominant performance. He ended the 2025 season seventh in the championship. In 2026 he continued with the Speed Up Racing organisation.
During the 2025 Valencia Test, Vietti made his MotoGP debut, substituting for the injured Franco Morbidelli with the Pertamina Enduro VR46 Racing Team aboard a Ducati Desmosedici GP24.
Vietti is one of the more consistent race winners of the modern Moto2 era, accumulating victories across different teams and machinery. His path through the VR46 Academy and CIV domestic racing to the World Championship reflects the depth of Italian junior motorcycle racing infrastructure. Though a world title has so far eluded him, his MotoGP test debut and sustained Moto2 presence into 2026 underline his standing among the leading Italian Grand Prix motorcycle racers of his generation.