De Leon was born in Drogheda, Ireland, and developed an early interest in motorsport through karting at international level. He contested the IAME Euro Series, the IAME Warriors Finale, and the British Kart Championship in 2021. He made his car-racing debut in the Radical SR1 Cup at the penultimate round of the 2021 season, winning two of three races at the final event. He also appeared in the 2021 Radical Intercontinental Cup at the Algarve International Circuit in Portugal, gaining his first exposure to international prototype competition.
In 2022 De Leon contested the Radical SR1 Cup full-time with Valour Racing and won the championship outright. He then entered the inaugural Radical Cup World Finals at Spring Mountain Motorsports Ranch in Nevada, United States, and won that event as well, completing a clean sweep of the Radical SR1 programme within a single calendar year. Alongside these results he made a one-off appearance in the 2022 GB4 Championship at the fourth round, finishing third on his debut and fifteenth in the partial-season standings. He additionally competed in the TGR Vios Cup Philippines in the Super Sporting Class, engaging with the national series of his Filipino heritage.
In 2023 De Leon won the Team HARD Scholarship, which awarded him a seat in the British Endurance Championship alongside a BTCC development role. He initially drove an Audi S3 at Silverstone before switching to a Porsche 991 GT3 Cup for the remainder of the campaign. Driving the Porsche he accumulated five wins, five podiums, and two pole positions and claimed both the overall British Endurance Championship title and the Class C trophy, an unprecedented double for a Team HARD Scholarship graduate in the series' history.
As part of his Team HARD Scholarship programme, De Leon was elevated to BTCC development driver status mid-season and replaced Jade Edwards from the sixth round, driving a Cupra León. He made 15 starts and scored six championship points, finishing 25th overall. The season gave him his first sustained experience of the physical contact, tyre strategies, and reversed-grid formats that define the British Touring Car Championship.
De Leon joined Duckhams Racing with Un-Limited Motorsport for 2024, again in a Cupra León. He completed all 30 races and accumulated 48 points, finishing 18th in the standings. The full-season campaign consolidated his knowledge of the BTCC's circuits and developed his ability to manage car condition across three-race weekends.
The decisive step in De Leon's career came with his move to West Surrey Racing and a switch to a BMW 330i M Sport LCI. At Brands Hatch Indy Circuit he converted pole position into a Race 2 victory, his first BTCC win. Over the course of the season he accumulated four podiums, two pole positions, and 149 championship points, finishing 13th overall. He won the Jack Sears Trophy — awarded to the leading driver who has not previously finished in the top six of the standings or won more than one race in a prior season — narrowly ahead of WSR teammate Charles Rainford.
De Leon remained with West Surrey Racing and the BMW 330i M Sport LCI for 2026. At the time of available data he held sixth place in the championship standings on 113 points, with the season still in progress.
De Leon is among the very few BTCC competitors of Filipino descent to have raced in the championship, and his trajectory from scholarship winner to BTCC race victor and Trophy holder within three seasons stands as one of the more rapid ascents through the British motorsport ladder system in the mid-2020s.