Gerard was born in Leicester into a family with strong ties to mechanical transport. The family business, Parr's Ltd., had begun as a bicycle manufacturer before moving into the motor vehicle market, though the firm concentrated on haulage rather than performance work. His father's preference for the sporting Riley brand gave Gerard his first motorsport experience: with a Riley Nine he entered the 1933 MCC Land's End trial, earning a Premier Award on his very first attempt despite severe short-sightedness.
Through the remainder of the 1930s Gerard competed in trials, sprint events and, after acquiring a 1½-litre Riley Sprite, circuit races. His home circuit was Donington Park in the East Midlands, where he took two victories over cars with considerably larger engines and finished ninth in the prestigious Donington TT. He drove in the Nuffield Trophy in both 1938 and 1939. In 1939 he also made the trip to Brooklands in Surrey, finishing third at the Opening Meeting and winning a Campbell circuit handicap race later in the year.
Towards the end of the war Gerard purchased ERA R4A from Reg Parnell for £1,000, and had it running in time for the Cockfosters demonstration in mid-1945. Before the 1946 season he also acquired ERA R14B, which he rebuilt and significantly modified for circuit racing. His principal engineering changes were to fit a preselector gearbox and replace the original Zoller-type supercharger with a smaller but more efficient Murray-Jamieson unit. He later reworked the bodywork, raking the radiator cowl to lower the bonnet line.
With R14B Gerard achieved the peak results of his career. Between 1947 and 1949 he scored three consecutive victories in the Empire Trophy and two victories in the Jersey Road Race. At the first post-war British Grand Prix in 1948 he drove the decade-old ERA to third place, beaten only by the brand-new works Maserati 4CLT/48s of Luigi Villoresi and Alberto Ascari. In 1949 he improved to second place, beaten only by the Maserati of Toulo de Graffenried. His two race victories, the Grand Prix second place, and a seventh in the 1949 International Trophy at Silverstone earned him the British Racing Drivers' Club Gold Star award for 1949.
Gerard continued with R14B into the inaugural FIA World Championship in 1950. At the very first Championship round — the 1950 British Grand Prix — he started from 13th on the grid and finished sixth, narrowly missing the points. At the Monaco event later in the same season he started 16th and again finished sixth, this time in R4A.
As the pace of technical development accelerated under Championship incentives, Gerard accepted that R14B had reached the end of its competitive life. He bought a Cooper T23-Bristol for 1952, and upgraded to the mid-engined Cooper T43 in 1957. In the Cooper years he finished in the Championship top ten only twice: in 1954 and at the 1957 British Grand Prix, which was his final World Championship appearance. He remained a consistent and respected force at British national level throughout the 1950s, winning at most major British circuits.
Gerard continued racing into the 1960s with a Turner sports car and used his engineering background to support other drivers as an entrant well into the 1980s. The owners of Mallory Park in his native Leicestershire honoured his contribution to the sport by naming the circuit's most prominent corner Gerard's. He died on 26 January 1990, one week after his 76th birthday, at South Croxton, Leicestershire.