Fornaroli began competitive karting around the age of ten. He first won the Mini Academy class of the Championkart championship in 2016, then moved to X30 Junior the following year. In 2018 he finished third in the Italian Karting Championship and entered the WSK Super Master Series. His final karting year, 2019, brought a third place in the prestigious Andrea Margutti Trophy and a front-running campaign in the WSK Euro Series on his OK-class debut. At the end of 2019 he was selected by ACI Sport and the Ferrari Driver Academy as one of five karting talents for the 16th edition of the Supercorso Federale event at Vallelunga.
Fornaroli made his single-seater debut in the 2020 Italian F4 Championship with Iron Lynx, scoring a fourth place on debut at Misano and recording eight top-five finishes across 20 races to finish ninth overall on 108 points, with a podium at Monza among his results.
In 2021 he remained with Iron Lynx alongside Ferrari Driver Academy recruit Maya Weug. Wins from pole at Misano and further podiums at Imola, the Red Bull Ring, and Mugello pushed Fornaroli into contention for the title against eventual champion Oliver Bearman before a difficult season finale at Monza — including a retirement and a DNS — dropped him to fifth in the standings on 180 points. He also made guest appearances in the 2021 ADAC Formula 4 Championship, scoring a third place at the Red Bull Ring.
Fornaroli stepped up to Formula Regional in 2022, first contesting a partial campaign in the Asian Championship with Hitech Grand Prix before joining Trident for the main European season. He scored points in fifteen of the twenty FREC races and finished eighth overall — the best-placed rookie — with a best result of fourth at the Hungaroring. He was also named the 2022 FREC rookie champion.
Fornaroli joined Trident for the 2023 FIA Formula 3 Championship, taking a first F3 podium with second in the Monaco sprint race and adding a third in the Barcelona sprint. He took his first pole position at Silverstone but finished second to teammate Oliver Goethe in the feature race. He ended the year eleventh overall on 69 points with three podiums and one pole.
Fornaroli returned to Trident for 2024. Consistent podium finishes including third at Imola, Barcelona, Budapest, and Spa built him into the championship fight. He went to the season finale at Monza as leader by a single point over Gabriele Minì. In the feature race, with the title on the line, Fornaroli found himself in fourth place on the final lap and needing to pass Christian Mansell. He threw his car down the inside at the final corner, claiming third without contact. Minì was later disqualified for incorrect tyre pressures, promoting Fornaroli to second and confirming the championship. He became the first-ever champion of FIA Formula 3 or its predecessor GP3 to not win a single race during the season, securing the title purely through consistency — he did not retire from any race and failed to score points in only two rounds.
Fornaroli made a brief F2 debut at the 2024 Yas Marina round as a substitute for Zane Maloney at Rodin Motorsport, without scoring points.
For the full 2025 season he joined Invicta Racing and balanced his racing campaign alongside university studies. He was immediately competitive, finishing second in the Melbourne sprint race and taking his first F2 pole position at Bahrain. Points followed steadily through Jeddah, Imola, and Monaco, where he finished second in the feature race. A stop-go penalty at Barcelona and a retirement ended a difficult triple-header on a low note.
His breakthrough win came at Silverstone, where a reverse-grid sprint pole allowed him to lead throughout from tenth on the qualifying order, holding off pressure from Kush Maini to take his first single-seater victory in four years. He followed that with a sprint win at Spa-Francorchamps and moved into the championship lead. At Budapest he overcut teammate Roman Staněk during the feature race pit stop cycle and won despite a five-second penalty for a pit-lane speeding infringement.
The Monza sprint saw Fornaroli pass Dino Beganovic for the lead and hold on for the win. He then qualified second at Baku before a penalty for contact with Alex Dunne compromised his weekend. At Lusail in Qatar, inheriting pole after an Oliver Goethe penalty, he finished second in the feature race — enough to clinch the championship with a round still remaining, becoming the fifth champion in the FIA Formula 2 era to hold F3 and F2 titles in consecutive years.
Fornaroli concluded the season with four wins, nine podiums, and three pole positions, with 211 points. He also received the Anthoine Hubert Award as the top rookie in F2. Formula Scout ranked him the best driver in junior formulae during 2025. His championship also helped Invicta Racing to back-to-back constructors' titles.
Invicta Racing team principal James Robinson noted that leading the championship by 17 points at the summer break while being unaffiliated with any Formula One team was "mind-blowing."
Following the F2 title, McLaren announced Fornaroli's entry into their driver development programme, then named him as a 2026 Formula One reserve driver alongside Pato O'Ward. He completed his first F1 test at the Circuit de Barcelona-Catalunya driving the McLaren MCL60, and tested the car again at Silverstone a month later.
In 2025 Fornaroli also made his Formula E debut in the Berlin rookie test at the Tempelhof Airport Street Circuit, driving for Jaguar TCS Racing.