Grant began racing as a privateer in 1969, entering the Manx Grand Prix on a Velocette 500cc. His first Isle of Man TT appearance followed in 1970, again on the Velocette, where he placed 18th in the Junior class. He progressed through early sponsorship by local businesses, including Clive Padgett of Padgetts of Batley and Brian Davidson of the John Davidson Group, competing on Yamaha TD2 250cc and TR2 350cc machinery. His early form on both two- and four-stroke machines marked him as an adaptable and technically capable racer.
Grant quickly earned a place in the reconstituted Norton factory team alongside Peter Williams and Phil Read — the first works Norton squad since the race shop was disbanded in 1962. In 1972 he partnered Dave Croxford to win the Thruxton 500 endurance race on a 745cc Norton Commando. He followed this with a second-place finish to Williams in the 1973 F750 TT, establishing himself as a front-runner at the senior level.
In 1974 Grant became the chosen rider for the Boyer Kawasaki Racing Team, a newly formed UK-based squad backed by Boyer of Bromley, a regional Kawasaki dealer. The association brought some of the defining achievements of his career.
In 1975 Grant became the first rider to complete a 120 mph lap of the North West 200 circuit. That same year he broke the absolute TT lap record for the Isle of Man Snaefell Mountain Course — a record that had been set by Mike Hailwood in 1967 on a 500cc Honda. Grant raised the average speed of one lap to 109.82 mph on a Kawasaki KR750 two-stroke triple, though he did not finish the race, retiring at the Gooseneck with a broken chain caused by a misaligned rear wheel spindle. He did win the 500cc Senior TT that year. In 1977 he raised his own lap record further to 112.77 mph, again on the 750cc Kawasaki.
Also in 1977, Grant won the Macau Grand Prix on the Kawasaki KR750, adding an important international road-racing victory to his record. He won the event a second time in 1984 on a Heron-Suzuki.
Grant entered the Grand Prix motorcycle racing circuit in 1977, racing for the Kawasaki factory team alongside teammate Barry Ditchburn. The following year he was joined by Kork Ballington and Gregg Hansford in the factory effort.
In 1979, Honda selected Grant to assist with the development of their ambitious oval-cylindered NR500 Grand Prix machine. The NR500 was a technologically unprecedented project, but its development proved difficult and the results were disappointing.
Grant's seven Isle of Man TT victories were accumulated across multiple manufacturers and machine types, demonstrating the breadth of his abilities. Among the notable machines he rode was Slippery Sam, a three-cylinder Triumph Trident, which achieved TT success and became one of the most celebrated motorcycles in the event's history. His seven wins placed him among the most successful riders of the 1970s, and his 1975 lap record remained a landmark in the event's history.
Mick Grant's career connected the classic era of British motorcycle racing — Norton factory teams, Triumph triples — with the rise of Japanese manufacturer dominance in the mid-1970s. His willingness to switch between manufacturers and machine types, combined with his record-breaking pace at both the Isle of Man TT and the North West 200, made him one of the most versatile and respected riders of his generation. He was known for racing with the number 10 and carried the initials JL on his helmet throughout his career as a tribute to his early sponsor and supporter, mechanic and frame-builder Jim Lee of the Dalesman marque — a personal tribute he retained even after retirement from competition.