To capture the American market, the 6T Thunderbird used a variant of the earlier Speed Twin's parallel twin engine, bored out from 500 cc to 650 cc to give the added horsepower American customers demanded. The concept of enlarging the Speed Twin, the Thunderbird name and its 'paper dart' logo were thought up by managing director Edward Turner on one of his regular trips to Triumph's operations in the USA. The 'paper dart' logo was embossed onto the chain case cover on Thunderbirds from 1955 to 1962, it appeared as a decal on the headlamp.

The 6T Thunderbird was launched publicly at Montlhery near Paris where three standard production bikes were ridden around a circuit by a team of riders who between them averaged a speed of 92 mph (148 km/h) over a distance of 500 miles (800 km). All three machines were ridden to the circuit and back to the Meriden factory.

Triumph obtained further publicity with Marlon Brando's 1953 motion picture, "The Wild One", in which he rode a 1950 6T Thunderbird. In the book Triumph Motorcycles In America (Brooke/Gaylin), there is reproduced a letter from Triumph's importers objecting to the producers as to the use of their machine in this film about rowdy motorcycle gangs.