Martin was born into a motorcycling family. His father Ian was a privateer racer who had competed at the Isle of Man TT, though he stopped racing after a crash at Oliver's Mount, Scarborough in 1988 when Martin was seven years old. Martin and his siblings attended every TT from birth until that incident. He attended school until 16 and completed an apprenticeship as a truck fitter, working for Volvo and later Scania centres in Grimsby. He continued working as a lorry mechanic throughout his racing career, treating television and racing as secondary to his trade.
Martin took up racing after a crash on public roads at age 18, and moved to Ireland to join Team Racing. He competed on road circuits for the first time at the Isle of Man TT in 2004, when he joined Uel Duncan Racing.
Martin joined Hydrex Honda for the 2007 season, a move that brought him into regular contention at the major international road races. At the North West 200 he collected multiple top-five finishes, and at the TT he consistently challenged for victories that eluded him. In 2008 he was leading the opening Superbike TT by eleven seconds when an electrical fault retired him on the fourth lap — the closest he came to breaking his TT duck.
From November 2010 he raced for TAS Racing, the Northern Ireland-based team that ran under various sponsor names including Relentless Suzuki, Tyco Suzuki, and Tyco BMW. At the 2010 TT he crashed heavily in the Senior race at Ballagarey, sustaining bruising to both lungs and minor spinal fractures. He recovered to continue racing the following season.
Martin won the Southern 100 Solo Championship on three consecutive occasions, joining Joey Dunlop as the only rider to achieve that feat. He achieved a hat trick of victories at the 2013 Ulster Grand Prix, winning the Supersport 1, UGP Superbike, and Superbike events. He suffered a further severe crash in the 2015 Dundrod 150 Superbike race, fracturing thoracic vertebrae, his sternum, several ribs, and a hand, requiring surgical rods in his back. He returned to racing in 2017 with Honda Racing, partnering John McGuinness, before retiring mid-season.
Martin accumulated 17 podium finishes at the Isle of Man TT across a career spanning 2004 to 2017, without achieving a race win. He broke his back twice in racing accidents — in the 2010 TT and the 2015 Ulster Grand Prix — and described pushing beyond his own risk threshold as a conscious choice in pursuit of victory. His fastest TT lap, set in June 2015 aboard the BMW S1000RR, was 132.398 mph, just outside the outright lap record at the time. He chose not to race the 2016 TT in favour of a mountain bike event, signalling a gradual shift in priorities.
Martin's media career began in earnest after his appearance in ITV4 programming around the 2009 TT, which led to work with BBC and Channel 4. He featured in The Boat that Guy Built (BBC, 2011), How Britain Worked (Channel 4, 2012), and the Channel 4 series Speed with Guy Martin, in which he pursued speed records across a variety of vehicles and disciplines. He starred in Closer to the Edge (2011), the documentary on TT racing, which brought him wide public attention. In August 2017, after retiring from racing, he joined the Williams Formula 1 team's pit crew at the Belgian Grand Prix.
Martin has written multiple books including his autobiography Guy Martin: My Autobiography (2014), which reached number one in the Sunday Times bestseller list, and several subsequent volumes. He was diagnosed with Asperger syndrome during the period of his media work, a finding he described as explaining certain patterns in his behaviour without changing anything in practice. He declined an invitation to join the relaunched Top Gear presenting team.
Martin attempted to set a motorcycle land speed record on the Triumph Rocket Streamliner at the Bonneville Salt Flats in 2016, but the attempt was abandoned following track conditions and a tip-over, with the project ultimately not progressing to a record run.
Martin's appeal rested on a combination of genuine mechanical ability, indifference to celebrity, and conspicuous bravery on fast public roads. His return to road racing in May 2019 at the Tandragee 100 showed an enduring connection to the sport even after formal retirement. As a rider who accumulated 17 TT podiums without a win, he is remembered as one of the most evocative figures of the modern road-racing era — a mechanic first and a public figure despite himself.