De Leon began karting in 2008 at Rye House Kart Raceway. His karting record included the Bizkart Rental Championship, the HKC Honda Clubman category, wins in the Motorsport UK British Kart Championship and UKC Ultimate Karting Championship finals, and the London Cup at Rye House. He also competed in the IAME Euro Series X30 Senior class in 2021, finishing 39th, alongside appearances at the IAME Warriors Finale and the British Kart Championship.
De Leon made his car racing debut in the Radical SR1 Cup at the penultimate round of 2021, immediately winning two of the three races at the final round at Donington Park. He also competed in the 2021 Radical Intercontinental Cup at the Algarve International Circuit in Portugal.
Competing full-time with Valour Racing in 2022, De Leon won the Radical SR1 Cup UK Championship, recording seven wins and nine poles across thirteen races. Later that year he won the inaugural Radical Cup World Finals at Spring Mountain Motorsports Ranch in Nevada, winning three of four races at the event. In 2023 he progressed to the SR3 Pro category of Radical Cup UK, winning the championship with four wins and eleven podiums from twelve starts.
De Leon entered a single round of the 2022 GB4 Championship with Valour Racing at Donington Park, finishing third on debut before placing eighth and ninth in the following two races. He finished 15th in the standings with 44 points.
In 2023, De Leon won the Team HARD Scholarship, which included an entry into the British Endurance Championship. He began the season in an Audi S3 before switching to a Porsche 991 GT3 Cup from the second round. He and his co-driver won the overall championship and Class C, accumulating 179 points from five starts with four wins and two pole positions.
De Leon joined the BTCC mid-season in 2023 as part of his Team HARD Scholarship package, taking over the race seat vacated by Jade Edwards after the fifth round. He drove a Cupra León for the remainder of the season, scoring 6 championship points from 15 starts and finishing 25th overall.
In 2024, driving for Duckhams Racing with Un-Limited Motorsport in a full BTCC season in a Cupra León, De Leon showed consistent improvement including a seventh-place finish at Brands Hatch. He also became the first BTCC driver to race on 100 percent sustainable fuel for the final nine events of the season. He finished 18th in the championship with 48 points from 30 starts.
For 2025, De Leon moved to West Surrey Racing, switching from front-wheel drive to the rear-wheel-drive BMW 330i M Sport LCI. He scored his first BTCC race victory in Race 2 at Brands Hatch Indy Circuit, and took two outright pole positions during the season at Knockhill and Silverstone. He added further podiums including a third place at Croft. He won the Jack Sears Trophy, narrowly edging teammate Charles Rainford. He finished 13th in the championship with 149 points from 29 starts.
De Leon returned with West Surrey Racing for 2026 in car number 2, and was running sixth in the championship standings after four rounds with podium finishes at Brands Hatch and Snetterton.