Clark was born in Leicestershire, the son of a motor dealer of the same name. After education at Hinckley Grammar School, he joined his father's business as an apprentice mechanic, gaining practical knowledge of cars before beginning to compete. He passed his driving test in 1956 and immediately joined the Leicester Car Club, where he met co-driver Jim Porter, who would navigate for him across the next twenty years.
Clark's early events were at club level in borrowed Ford cars. By the early 1960s, after switching to a BMC Mini Cooper, he and Porter began winning, taking the East Midlands Rally Championship in 1961 and 1962 and recording top finishes in the International Circuit of Ireland and the Motoring News Championship.
Early success led to works opportunities. Clark drove a Triumph TR4 for the Spa-Sofia-Liege in 1963 and a Reliant Sabre in the Alpine Rally. He then agreed a two-year works deal with Rover, winning his Monte Carlo Rally category in a Rover 2000 in 1965 and taking his first British Rally Championship title that same year.
In 1964 Clark also won the first of six Scottish Rally victories in his private Ford Cortina, a tally that remains one of his most impressive career statistics.
In 1966 Clark and Porter signed to the Ford of Britain works team, and the partnership lasted fifteen years. Ford's rally programme was sponsored by Esso Uniflo, with Clark forming part of a three-driver lineup alongside Vic Elford and Bengt Soderstrom, initially using Ford Cortina GTs. In 1968 Clark switched to the Ford Escort RS, the car he would become most closely identified with, using works versions until 1979 and then private entries into the 1980s.
Clark and Porter won the British Rally Championship again in 1972, 1973, and 1975. They also won the Acropolis Rally in 1968 and the Circuit of Ireland in 1970 and 1971, bringing their total victories to 40 at national and international level.
Clark's most significant wins came at the RAC Rally, the United Kingdom's premier rally. He won in 1972 alongside co-driver Tony Mason, and again in 1976 with Stuart Pegg — the latter win coming when the RAC Rally was part of the World Rally Championship calendar, making Clark the first British driver to win a WRC event. This achievement went unmatched by a British driver for over fifteen years. Porter could not co-drive for Clark's RAC wins because of his contractual obligations to the rally organisers, requiring Clark to use different navigators for each RAC victory.
In 1973 Clark led the East African Safari Rally by over an hour before being forced to retire at the halfway stage with a disintegrating car, underlining both his speed and the fragility of machinery under extreme conditions.
Clark received the Segrave Trophy in 1975, together with Porter, awarded to the Briton demonstrating the most outstanding achievement in transport. He was appointed MBE in 1979.
Clark competed in rallycross with Ford Capris between 1969 and 1971, and also drove unusual models including a Ford Zodiac in Eastern Europe and a Ford Capri in the Tour of Britain as part of his extended development contract with Ford. After the arrival of the four-wheel-drive Audi Quattro era, Clark's competitive opportunities at works level diminished, and he returned to club rallying before establishing Roger Clark Motor Sport, a car preparation business run by his son Matt that continues to operate.
Clark died on 12 January 1998 from the effects of a stroke. A bronze statue was later erected in his memory at Mallory Park.
In 2004 a historic rally event was established in Clark's honour, recreating the route of the classic five-day RAC Rally across Scotland and northern England, using stages including Kielder Forest and Grizedale Forest that no longer feature on the modern WRC itinerary. Competitors are restricted to vehicles built before 1982. The event was held annually until 2014 and on odd years from 2017 onwards.