Junior career Manzi joined the
2012 Red Bull MotoGP Rookies Cup, and had two podiums in his first season already, a 2nd place at the
Sachsenring and a 3rd place at Brno. He ended his rookie campaign with 75 points, and 13th in the standings. He returned for both
2013 and
2014, finishing 2013 third in the competition with four 2nd places, and three 3rd places, and again finished third in 2014, with one victory, two 2nd places, and six 3rd places.
Moto3 World Championship San Carlo Team Italia (2015) Manzi made his debut in the
2015 Moto3 World Championship, racing from the second round of the season onwards, after being replaced for the opening event by
Marco Bezzecchi due to age limits. Riding on a
Mahindra MGP3O entered by San Carlo Team Italia, alongside his compatriot
Matteo Ferrari, he finished in the points four times, his best result being a twelfth place in
Aragon. He ended his rookie year 27th in the standings with 10 points.
Mahindra Racing (2016) In the
2016 season, Manzi appeared in three races as a
wild card, scoring a 20th place in Austria, a 4th place at
Silverstone, and a 16th place in Rimini. He ended the season 29th in the standings, with 13 points, all 13 coming in Silverstone.
Moto2 World Championship Sky Racing Team VR46 (2017) In
2017, Manzi moved up to the Moto2 class with
Sky Racing Team VR46 alongside fellow Italian
Francesco Bagnaia, riding a
Kalex. Manzi finished in the points four times, his best result a 7th place at
Silverstone, overall finishing the year with 14 points, 25th in the standings.
Forward Racing Team (2018) For
2018, Manzi switched to
Forward Racing, swapping places with
Luca Marini who went to
Sky Racing Team VR46. Manzi had a bad year, finishing in the points only twice out of 15 races (a 10th place in France, and a 14th place in Austria), before being involved in a nasty crash during the race in Misano, where
Romano Fenati reached over, and pulled Manzi's brakes at 200 km/h. Manzi managed to stay on the bike, but later crashed out on his own, while Fenati was black-flagged and disqualified from the race. Although after the race Fenati was given a two race ban, his contract was terminated with immediate effect by the Rivacold Snipers team, and Manzi raced the following two weekends since he wasn't injured in the accident; when Fenati came back following his two race ban, Manzi sat out the remainder of the season, stating that "I don't feel safe with riders on the track trying to kill me." Manzi finished the year with 8 points, 24th in the championship.
MV Agusta Forward Racing (2019–2020) Manzi stayed with
Forward Racing for the
2019 season, but was now riding
MV Agusta bikes. He had a better season than 2018, finishing in the points seven times, four times in the top-10, including a 7th place in Assen, and a 4th place in the season closer round at Valencia. Manzi ended the season 19th in the rider's championship, with 39 points. In his final year with Forward Racing, the
2020 season saw Manzi grab his first pole position in the category, at the penultimate round in Valencia, marking the first pole position of Forward Racing since 2010, and the first pole position of MV Agusta in 44 years. He retired from the race, ending his season with eight point scoring finishes, a best result of 9th in Jerez, and 22nd overall in the championship with 21 points.
Flexbox HP40 (2021) Riding for
Pons Racing in
2021, alongside
Héctor Garzó, Manzi had another average year, with seven point scoring finishes, three top-10 finishes in Doha (8th), Mugello (10th), and Misano (6th), ending his last season of Moto2 with 36 points, 19th in the standings.
Yamaha VR46 Master Camp Team (2022) Manzi replaced
Keminth Kubo for this team.
Supersport World Championship Dynavolt Triumph (2022) Manzi competed in the
2022 Supersport World Championship, with the Dynavolt Triumph. ==Career statistics==