Isack Alexandre Hadjar was born on 28 September 2004 in Paris, France, to an Algerian family of physicians and physicists. His father, Yassine Hadjar, is a researcher in quantum mechanics and also served as his kart mechanic. Isack is named after famous physicist Isaac Newton.
Hadjar started competitive kart racing in 2012. After initially competing in national championships, Hadjar progressed to the international scene in 2017. He competed in the 2018 Karting World Championship and finished 22nd.
In 2019, Hadjar made his single seater debut in the French F4 Championship. Despite struggling to push down fully on the car's pedals owing to his low height at the start of the season, Hadjar was able to achieve his first single-seater win at Spa during the third round. He finished seventh in the standings, claiming second in the junior class.
Hadjar made his debut at the Formula Regional level in 2021, competing in the first three rounds of the F3 Asian Championship with Evans GP. He then competed in the Formula Regional European Championship, where he partnered Zane Maloney, Léna Bühler and fellow countryman Hadrien David at R-ace GP. Hadjar ended up fifth in the standings, just four points behind teammate Maloney, and won the honours for the best rookie of the season.
Hadjar started his season out in the best way possible, inheriting victory in the Sakhir sprint race after original winner Oliver Bearman had received a five-second time penalty for track limits infringements. He finished fourth in the drivers' standings, with three wins, one pole, five podiums and 123 points.
Hadjar joined Hitech Grand Prix for the 2023 Formula 2 season alongside his then fellow Red Bull junior Jak Crawford. He finished the year 14th in the drivers' standings with 55 points, two behind teammate Crawford. In 2024, Hadjar switched to Campos Racing for the 2024 Formula 2 season, teaming up with fellow Red Bull junior Pepe Martí. He ended his final F2 season as runner-up in the Drivers' Championship finishing with four wins, eight podiums, one pole position, one fastest lap and 192 points.
Hadjar made his free practice debut at the 2023 Mexico City Grand Prix with AlphaTauri, to fulfill the mandatory rookie driver rule. He was promoted to replace Liam Lawson as the reserve driver for both Red Bull and the rebranded Racing Bulls. Hadjar partnered Yuki Tsunoda at Racing Bulls for 2025. He qualified eleventh on debut at the Australian Grand Prix, before spinning into the barriers on the formation lap and failing to start the race. He scored several points finishes across his rookie season, including his maiden podium at the Dutch Grand Prix. Hadjar was promoted to the senior Red Bull team in 2026 alongside Max Verstappen.
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