Davies began racing in the British Mini Moto championship in 1995 and progressed through junior road racing before entering the Aprilia Challenge 125cc Championship in 1999 at the age of 12, receiving special dispensation to compete. He finished sixth overall and was the only rider to complete every race in a points-scoring position, earning the Superteen of the Year award and setting a new lap record at Donington Park National circuit.
In 2001, Davies became the youngest winner of a British Championship race, taking victory in the British 125 Championship at Thruxton at 14 years and 5 months old. He also contested the Spanish National 125 Championship under the management of Alberto Puig and was nominated for BBC Young Sports Personality of the Year.
By 2002, Dorna Sports placed Davies with Team Matteoni Racing in the 125cc Grand Prix World Championship, where he became the youngest rider to compete in a full season of GP motorcycle racing. He continued in the 250cc class with Aprilia Germany from 2003, becoming the youngest rider to score World Championship points in that class. He showed strong results at the end of 2004, finishing ninth in Malaysia, sixth in Australia, and fifth at Valencia on customer machinery that was inferior to factory bikes.
Davies moved to the AMA Supersport Championship in 2007, racing a Yamaha for the Celtic Racing team. The following year he rode a Kawasaki for Attack Kawasaki and was named winner of the 2008 Daytona 200 after original race winner Josh Hayes was disqualified, making Davies the first rider from the United Kingdom to win that prestigious event.
In 2007, Davies made his MotoGP debut at Mazda Raceway Laguna Seca as a replacement for injured Alex Hofmann with Pramac d'Antin Ducati. He later replaced Hofmann for the final three rounds of the 2007 season. Though his results were modest, Ducati offered him a full-time testing role for 2008, which he declined in favor of returning to AMA competition.
Davies joined Triumph in World Supersport late in the 2009 season and remained with the brand for 2010, consistently proving to be their fastest rider and securing several podium finishes. A move to Yamaha machinery for 2011 transformed his season entirely. After a difficult opening round due to a puncture, Davies won six races and claimed eight podiums on his way to the 2011 World Supersport Championship title. The same year he was named BBC Wales Sports Personality of the Year.
Davies stepped up to the Superbike World Championship in 2012 with ParkinGO MTC Racing Aprilia, impressing in his debut season with four podiums including one race win and ninth place overall. A move to the factory BMW Motorrad Goldbet team followed for 2013.
From 2015 onward, Davies became one of the defining riders of the Ducati Aruba.it factory team. He was a consistent race winner and title challenger, finishing as runner-up in the championship on three occasions. His combination of aggression, mechanical sympathy with the Ducati package, and circuit knowledge made him a perennial front-runner.
Davies announced his retirement from regular competition in September 2021 after years at the sharp end of the World Superbike field.
From 2022, Davies took on a rider-coach role working with Ducati and Feel Racing, mentoring riders including Alvaro Bautista, Michael Ruben Rinaldi, and Nicolo Bulega. He also competed in endurance racing, entering the 2023 24 Hours of Le Mans with David Checa and Philipp Ottl aboard an ERC Endurance Ducati, finishing fifth.
In 2024, Davies returned to competitive riding as a confirmed entrant in the MotoE World Championship, an electrically powered race series using Ducati machinery, demonstrating his continued appetite for competition in a new format.
Davies stands among the most significant Ducati riders of the modern Superbike World Championship era. His three runner-up finishes in the premier class, combined with his World Supersport title and his adaptability across multiple series and continents, mark him as one of the most complete motorcycle racers of his generation.