Tandy was born in Bedford and began racing as an eleven-year-old in Ministox short-oval machinery in 1996, winning the Midland regional title immediately. He graduated through successive championships — Ministox, Mini Se7ens, the BRDC Single Seater Championship — before arriving in the British Formula Ford Championship in 2006, where he finished runner-up in his debut season. At the end of 2007 he won the Formula Ford Festival after series champion Callum MacLeod received a post-race penalty, settling a season-long battle with James Nash by just twelve points.
His Formula Three years (2008–2009) were spent with his brother Joe's team on an unfavourable Mygale chassis. Despite the equipment disadvantage Tandy recorded multiple podiums and earned a reputation for single-lap pace, posting four fastest laps from the first eight races in 2009. Eighteen days after his brother Joe died in a road accident in May 2009, Tandy gave the team its first win at Rockingham, driving away from the field by more than eight seconds.
After impressing in cameo appearances in the Porsche Carrera Cup Germany and Porsche Supercup in late 2009, Tandy joined Konrad Motorsport for a full 2010 Porsche Mobil 1 Supercup campaign, taking his first Supercup win at Silverstone and pushing eventual champion René Rast to the final round at Monza. He won the German Carrera Cup title in 2011. His consistent performances earned him Porsche factory status, confirmed officially in late 2012.
Tandy joined the Porsche factory programme at the 2013 24 Hours of Daytona and quickly established himself as a front-rank endurance driver. He won the GT class at the 2013 Petit Le Mans with Team Falken Tire and claimed the GTLM class victory at the 2014 Rolex 24 at Daytona sharing with Richard Lietz and Patrick Pilet for Core Autosport.
The 2015 season brought his most celebrated results. Partnering Pilet in the IMSA WeatherTech SportsCar Championship, he claimed four wins and helped Pilet to the drivers title. At Le Mans that year, he joined Nico Hülkenberg and Earl Bamber in the Porsche 919 Hybrid LMP1 entry, and the No. 19 car won overall — Tandy's first Le Mans triumph. He also took the overall win at the 2015 Petit Le Mans.
Tandy returned to Porsche's LMP1 squad for the 2017 FIA World Endurance Championship, scoring multiple podiums. When Porsche exited prototype racing after 2017, he returned to IMSA full-time in the No. 911 Porsche 911 RSR alongside Pilet, earning two wins in 2018 and runner-up status in 2019 with three victories. That 2019 Le Mans he finished third overall alongside Earl Bamber.
For 2020 he paired with Frédéric Makowiecki in the No. 911, adding two IMSA wins and a Spa 24 Hours overall victory. Corvette Racing signed him for 2021; sharing with Tommy Milner, Tandy claimed four wins and the GTLM runner-up in IMSA. In 2022 he competed in the FIA World Endurance Championship for Corvette, taking a class win. He returned to Porsche for 2023 in the new 963 prototype.
Tandy's Nürburgring 24 Hours overall win came in 2018, adding to his Le Mans victory. The Spa 24 Hours overall followed in 2020. The Daytona 24 overall in 2025 completed the Grand Slam — a clean sweep of every major 24-hour event, a feat no driver had previously accomplished. Victory at the 2025 12 Hours of Sebring extended the record further, making him the only driver with overall wins at all six of the sport's most prestigious endurance races.
Tandy's career charts a path from short-oval British grassroots racing to the pinnacle of endurance sport. His personal story — continuing to race for his late brother's team in the weeks after Joe's death — reflects a resilience that marks his entire approach. As a Porsche factory stalwart across more than a decade, he won in LMP1, GTE, and GTP machinery and became one of the defining endurance drivers of his generation.