Hill's early career included a near-fatal motocross accident that cost him a kidney and his spleen. The health consequences shaped his entire career, requiring him to take penicillin daily and leaving him vulnerable to illnesses such as food poisoning that disrupted his racing schedule in 2006. His brother Jimmy also competed in motorcycle racing.
Hill switched to road racing in 2001 and earned his first BSB ride by winning the Virgin Mobile Yamaha R6 Cup in 2003, completing every race in the series.
In his debut BSB season in 2004 with Virgin Yamaha, Hill became the youngest rider ever to start a race from the front row of the grid. He was the only one of the team's four riders retained for 2005, a decision team boss Rob McElnea attributed to Hill having proved himself beyond expectations.
Hill claimed his first BSB win at Cadwell Park in 2005. In 2006 he entered the World Superbike Championship round at Silverstone as a wildcard, stunning experienced regulars by taking pole position in changeable qualifying conditions before finishing both races in the points. He finished eighth in the BSB standings that year.
For 2008 Hill switched to the World Supersport Championship full-time with the Hannspree Althea Honda team. His season became catastrophic: he crashed on his very first test, breaking his femur, ankle, and hand, missing the opening five rounds. On his return at the Nurburgring, he was involved in a pile-up triggered by a wildcard rider at turn one, rebreaking his femur and ending his season entirely.
The Althea team retained Hill for 2009 in the World Superbike Championship, but he was uncompetitive and lost his ride mid-season. He joined Worx Crescent Suzuki as a replacement for the injured Sylvain Guintoli, delivering competitive performances before Guintoli's return ended his stint. He finished the season with Hydrex Honda in BSB, gaining strong results including podium finishes at Oulton Park.
Hill joined Worx Crescent Suzuki full-time for 2010 alongside Yukio Kagayama. He won the season opener at Brands Hatch and led the championship by 36 points at one stage. Difficult rounds at Cadwell Park and Knockhill eroded his lead, though he recovered with three podiums at Snetterton. Hill was a central subject of the documentary film I, Superbiker, which followed his 2010 BSB campaign.
Hill signed with Swan Yamaha for 2011 alongside supersport champion Michael Laverty. He started the season strongly with a win at Brands Hatch Indy in the second race of the opener and led the championship early on. A shoulder injury sustained at Oulton Park when oil dropped by a crashing Loris Baz caused Hill to fall briefly threatened his season, but he recovered. A historic double win at Knockhill Racing Circuit was a highlight on his way to the 2011 British Superbike Championship title.
Hill retired from professional racing at the end of 2012 and worked as a self-employed graphic designer. He announced in late 2014 that he would manage a British Superbike team for 2015 under the Be Wiser Kawasaki banner, though he departed in August 2015 and the team folded in September. Hill subsequently launched his own outfit, Tommy Hill Motorsport (THM), for 2016 with Yamaha R1 machinery, fielding riders John Hopkins and Stuart Easton under backing from ePayMe.
Hill's 2011 BSB title marked him as one of the most determined riders of his generation, having overcome multiple severe injuries to reach the pinnacle of domestic British superbike racing. His transition into team management, albeit brief, reflected a continued passion for the sport beyond his riding career.