The Isle of Man TT became the British round of the motorcycle Grand Prix world championship in 1949.
That year marked the inauguration of the FIM Motorcycle Grand Prix World Championship, the predecessor of today’s MotoGP series. The Isle of Man TT was selected as the championship’s British venue, giving the island’s road race an official place on the international calendar. Its long, public-road circuit and prestige made it one of the championship’s major events.
The TT remained the British round from 1949 through 1976. During that period, races on the Mountain Course contributed to the Grand Prix championship, although the event was also an important independent fixture with its own traditions, classes and identity.
The answer is sometimes confused with 1977, when the British Grand Prix moved to the mainland at Silverstone after the TT’s final world-championship appearance. The year 1954 is also relevant to TT history because the Sidecar TT and Ultra-Lightweight TT were reintroduced then, but it was not the start of the championship relationship.