Born in Torino (Italy), Bagnaia was successful in Minimoto and he won the European MiniGP championship in 2009. Bagnaia made his preGP 125 Mediterranean championship debut with Monlau Competicion team in 2010 and finished 2nd in the championship. In the 2012 CEV Moto3 season he rode a Honda NSF250R and finished 3rd in the championship behind Álex Márquez and Luca Amato with three podiums in seven races. Bagnaia is also a member of the VR46 riders academy.

In 2013, Bagnaia made his Grand prix debut with Team Italia FMI with Romano Fenati as his partner riding a Honda. The season was a disappointing year for Bagnaia as he did not manage to get a single point in the 17 races he participated in. His best race was a 16th-place finish at Sepang.

In 2014, Bagnaia switched team to join the newly formed Sky Racing Team by VR46 riding a KTM with same partner Romano Fenati. After failing to score points in his rookie season Bagnaia made a clear improvement after a strong pre-season and also switching bikes for the season, riding a KTM instead of Honda. He finished top 10 five times during the first 7 races with a 4th-place finish at Le Mans as his best result, where he also set the fastest lap of the race. Bagnaia missed the races at Assen and Sachsenring due to injury. After scoring 42 points in the first 7 races of the campaign Bagnaia slumped badly during the second part of the season, only finishing in the points twice of the last 9 races, clearly affected by his injury. He finished the season in 16th position with 50 points.

In 2015, Bagnaia made another team and bike change, this time joining Aspar Racing Team on a Mahindra and new teammates Juanfran Guevara and Jorge Martín where he got his first podium at the Le Mans finishing the race in 3rd place behind Romano Fenati and Enea Bastianini. In the next race at Mugello Bagnaia finished 4th, missing the podium with 0.003 seconds. He was on his way to another podium finish at Silverstone but crashed with 2 laps remaining, fighting with Niccolò Antonelli for the 3rd place. Despite improving his championship position with two places and gaining 26 more points than the previous year on a new bike for the third straight season, this time a Mahindra it was still an up and down year for him. Bagnaia only finished Top 10 during races five times. He also missed points in seven races, unclassified in five of those. He finished the season down in 14th place with 76 points.

In 2016, Bagnaia started the season with a podium finish at Losail and another podium finish at Jerez, finishing 3rd on both occasions. At his home race in Italy Bagnaia secured another 3rd position beating Niccolò Antonelli by 0.006 seconds. Followed by a crash at Barcelona, Bagnaia secured his first Grand Prix win at the historic Assen circuit in his 59th Moto3 race and it was the first win for Mahindra too. He now had 4 podiums in the first 8 races of the season and found himself fighting for the title. After two average races and a crash at Brno, Bagnaia got his first pole position in the rain-affected Silverstone and finished second behind Brad Binder in a thrilling race. Bagnaia won his second race of the season at Sepang, winning the race comfortably with a big gap after Brad Binder, Joan Mir and Lorenzo Dalla Porta all crashed out in the same corner during the beginning of the race, which was filled with multiple crashes. He finished the season with 145 points to place 4th in the Moto3 Championship with a total of 2 wins and 6 podiums. Bagnaia had an opportunity to finish 2nd in the World Championship behind Brad Binder but was unfortunately taken out in both Phillip Island and Valencia by Gabriel Rodrigo. Rodrigo pushed out Fabio Di Giannantonio in Australia who went down and collected Bagnaia with him. In Valencia Rodrigo made a highside crash on the first lap approaching the last corner, again Bagnaia went down unavoidably.

After 4 seasons in the Moto3 category Championship, Bagnaia moved up to Moto2, racing for SKY Racing Team VR46, where he last rode in 2014, with Stefano Manzi as his teammate. In just his fourth ever Moto2 race at Jerez Bagnaia finished 2nd. He finished 2nd in the next race as well at Le Mans after having qualified in 2nd place, missing pole position to Thomas Lüthi by just 0.026 seconds. Bagnaia took a third podium at Sachsenring, finishing 3rd behind Franco Morbidelli who won the race and Miguel Oliveira who came in second. At Misano Bagnaia originally finished the race 4th behind Dominique Aegerter, Thomas Lüthi, and Hafizh Syahrin however Aegerter was later disqualified promoting him to his 4th podium of the season. He was crowned Moto2 Rookie of the year after the Japanese Grand Prix at Motegi. He finished his rookie season with 174 points to place 5th in the Moto2 Championship, scoring points in 16 of the 18 races.

Bagnaia opened the season with a win in Qatar, having led the race from start to finish. Bagnaia took a second win in Austin after a hard fight with Álex Márquez winning the race with a gap of 2.4 seconds and also setting the fastest lap of the race. At Jerez Bagnaia finished 3rd behind Lorenzo Baldassarri and Miguel Oliveira holding his starting grid position. Bagnaia took his first pole position in Moto2 at Le Mans, like the race in Qatar he led from start to finish. The win was also his 3rd podium at Le Mans since 2015. Bagnaia took a 4th win at Assen, starting the race from Pole Position and leading the entire race. After qualifying 3rd on the grid in Sachsenring Bagnaia finished the race down in 12 place, having been forced outside of the track after Mattia Pasini fell down in front of him in the last corner on the second lap, despite being down in 26th position he still made up fourteen places, including overtaking Álex Márquez on the final lap in the last corner. At Brno Bagnaia finished third and lost the championship lead to Oliveira. He retook the championship lead at Austria, winning his 5th race of the season. Bagnaia won his sixth race of the season at Misano from pole position. He took a 5th straight podium at Buriram, winning the race with his teammate Luca Marini in second place. He took his 8th win of the season at Motegi after Fabio Quartararo who initially won the race was disqualified due to low tyre pressure. After finishing 3rd at Sepang he was crowned Moto2 World Champion with his 12th podium of the season, his teammate Luca Marini took his first ever Moto2 World Championship win as well, his 5th podium of the campaign.

Bagnaia finished every single Moto2 race he participated in, 36 in total. He scored points in 34 of them and was on a 30 race point scoring streak, starting from Barcelona in 2017. The streak ended when he retired from his first MotoGP race at Losail.

After two seasons in the Moto2 category championship, Bagnaia was promoted up to MotoGP with Pramac Ducati. He was, in fact, offered a ride in MotoGP in 2018 with the same team after his stellar rookie season in 2017, where he took four podiums and finished 5th in the championship behind Franco Morbidelli, Thomas Luthi, Miguel Oliveira, and Álex Márquez but eventually decided to stay, with an opportunity to take the championship title. He replaced fellow Italian rider Danilo Petrucci, who went to the Factory Ducati Team, replacing Spaniard and three time MotoGP World Champion Jorge Lorenzo who took the seat vacated at Repsol Honda Team by Dani Pedrosa after he decided to retire after 13 seasons in MotoGP, from 2006 to 2018 to become an official test rider for KTM.

After failing to score in Qatar where he retired from the race due to a damaged front wing Bagnaia took his first two points in the MotoGP World Championship with a 14th place in Argentina, having started the race from 17th on the grid. Bagnaia finished 9th in Austin getting positions after both Marc Marquez and Cal Crutchlow crashed out from the race in separate accidents. Both Maverick Vinales and Joan Mir jumped the start and was subsequently penalized with ride through penalties. Prior to the fourth race at Jerez Bagnaia had three straight podium finishes, starting from 2016. He qualified 10th on the grid however he crashed out on the sixth lap, fighting with Pol Espargaro. At Le Mans where Bagnaia won the race in Moto2 in 2018 he crashed out on the sixth lap after an incident with Maverick Vinales. In the next race at Mugello, his home Grand Prix Bagnaia had a solid start to the weekend. He topped the second Free Practice time sheets on his way to qualify 8th on the grid. However he crashed in the last corner on the 11th lap in seventh place. It was the first time in Bagnaia's career that he had failed to finish three races in a row, all of them with crashes. In Austria Bagnaia had his best race weekend since his time in Moto2, both in terms of his qualifying and race. He managed to advance to Q2 alongside Cal Crutchlow where he subsequently qualified 5th on the grid. He later finished the race in 7th place. At Phillip Island Bagnaia finished the race in 4th place, missing the podium with just 0.055 seconds behind his teammate Jack Miller.

Bagnaia finished his rookie season with 54 points, placing him 15th in the championship standings. He missed the final race at Valencia due to injury.