Plater briefly raced speedway in his teens before starting his working life as a bricklayer. He took up circuit racing in 1994 and won his first race at Cadwell Park. By 1998 he had won the British Powerbike championship, though he narrowly missed the British Supersport title that year, losing it on countback. He demonstrated international endurance potential at the 1999 Bol d'Or, where he finished third on a Kawasaki — a result that earned him a full-time British Superbike ride for 2000.
Plater competed in the British Superbike Championship across multiple seasons, riding for various teams. His 2000 campaign on the Kawasaki produced a sixth-place overall finish without podiums but with consistent mid-field results. Injury disrupted 2001, though he still managed three podiums. His strongest superbike season came in 2002 on a Yamaha, finishing fifth overall with two late-season wins. In 2003, riding a Honda, he added another win at Cadwell Park and finished sixth.
Plater missed the start of 2006 through injury, but returned in striking fashion by winning both Superbike races at that year's North West 200 road race.
Plater's most notable achievements came on the roads circuits. At the 2007 Isle of Man TT he was voted Best Newcomer, having been mentored by former racer Mick Grant. The following year, 2008, he won the Supersport TT race after the on-the-road winner Bruce Anstey was excluded following a technical infringement.
The 2009 Isle of Man Senior TT was Plater's defining roads victory. Riding for the HM Plant Honda team, he set a new race record and beat teammate John McGuinness to the win after McGuinness's chain broke on the fourth lap. In the same 2009 season he also won the North West 200, making it a memorable double on the roads in addition to his British Supersport championship title that year.
In 2010, during Thursday practice for the North West 200, Plater crashed at Quarry Hill on the Coast Road section. He suffered a broken arm, and subsequent hospital examinations revealed he had also fractured his neck. The severity of the injury marked the beginning of the end of his front-running racing career.
Plater spent the 2009 season with HM Plant Honda in the British Supersport Championship, winning the title ahead of Australian Billy McConnell at the final round. During that campaign he also stood in on a Superbike at Brands Hatch when Josh Brookes' visa was delayed — falling from the lead in race one before recovering to finish third in race two. He additionally contested the Le Mans 24 Hour motorcycle race for Honda France in 2009.
Plater had a sustained involvement in endurance racing. He set a strong pace at the 1999 Bol d'Or and won the 2007 Albacete 6-Hour race on a Kawasaki, partnering Julian Mazuecos and Gwen Giabbani. In 2011 he confirmed his retirement from road racing to concentrate on the FIM Endurance World Championship.
After retiring from front-line competition, Plater became a motorcycle racing co-commentator and presenter. In 2015 he was appointed manager of the Prime Factors Racing team for road racing and endurance competition, while continuing to participate in demonstration events. He became a co-host of The TT Podcast, in which he interviews riders and figures associated with the Isle of Man TT. Plater lives in Woodhall Spa, Lincolnshire, where he is also involved in property development.
Plater's career encompassed the full breadth of British motorcycle racing — circuit championships, international road races, and endurance events. His 2009 season, combining the British Supersport title, a Senior TT record-breaking win, and a North West 200 victory, stands as one of the most productive single-year achievements by a British road racer of his generation.