Hughes began racing in karting in 2010 and spent two years in the Super 1 National Formula KGP Championship. In 2012, he made his single-seater debut in the Formula Renault BARC Championship with Antel Motorsport.
Hughes moved to the newly created BRDC Formula 4 Championship in 2013 with Lanan Racing, taking four wins and six further podiums to clinch the title, beating Seb Morris by 35 points. As a reward, he tested a Dallara F308 for Carlin at the Circuit Ricardo Tormo.
In 2014, Hughes competed in the Formula Renault 2.0 Northern European Cup and made part-time appearances in the Eurocup Formula Renault 2.0 and Formula Renault 2.0 Alps. For 2015, he raced full-time in both Eurocup and Alps with Koiranen GP. He took victory in the second Spa race in the Eurocup, finishing sixth overall, while in the Alps he won at Spa, Monza, and Misano and led the championship entering the final round. He ultimately lost the Alps title to Jack Aitken by five points, a defeat he later attributed to competing with a cracked chassis in the final round.
Hughes graduated to the GP3 Series in 2016 with DAMS, earning his first victory in the Hockenheim sprint race and a second win at Abu Dhabi to finish the year strongly. He returned to GP3 in 2018 with ART Grand Prix after a year in FIA Formula 3, taking one win at the Red Bull Ring and ending eighth in the standings.
For 2017, Hughes joined Hitech GP in the FIA Formula 3 European Championship, winning at the Nürburgring and finishing fifth overall.
He continued in the FIA Formula 3 Championship in 2019 with HWA Racelab, scoring a win at the Red Bull Ring and finishing seventh. He returned in 2020, still with HWA Racelab alongside Enzo Fittipaldi and Jack Doohan, winning at Barcelona and Monza on his way to seventh place for a second consecutive year, scoring 111.5 of his team's 138.5 points.
Hughes made two partial Formula 2 campaigns in 2020 and 2021 as a substitute for HWA before joining Van Amersfoort Racing full-time for the 2022 season alongside Amaury Cordeel. He took a sprint-race podium at Jeddah before disqualification, then scored a best finish of fourth in the feature race. A crash in Monaco qualifying, a COVID-19 absence covering the French and Hungarian rounds, and growing Formula E commitments complicated his season; he left VAR before Spa-Francorchamps and ended sixteenth in the standings.
During the 2023 London ePrix weekend, Hughes set a Guinness World Record for indoor speed, hitting 218.71 km/h inside London's ExCeL Centre driving a modified Formula E Gen3 car called the GENBETA.
After reserve and development roles with Venturi Racing and Mercedes-EQ, Hughes joined the McLaren Formula E Team for the 2022–23 season alongside René Rast. He claimed two pole positions during the campaign and scored consistently in the early rounds, ending twelfth in the standings with 48 points. He remained at McLaren for 2023–24 alongside Sam Bird, achieving a career-best fourth place at the second Diriyah ePrix before McLaren did not retain him for a third season.
Hughes then signed a multi-year deal with Maserati MSG Racing for the 2024–25 season, partnering 2021–22 champion Stoffel Vandoorne. Despite the multi-year announcement, he did not continue with the team beyond that campaign. He subsequently signed with Mahindra Racing as a test and reserve driver for the 2025–26 season. In June 2025, he also completed a Formula One test for McLaren at Barcelona, driving the McLaren MCL60.