MG began offering the MGB GT V8 in 1973 powered by the aluminium block 3,528 cc Rover V8 engine, first fitted to the Rover P5B. This engine had been used in the unibody GM 1961–1963 A-body platform Buick Special/Skylark and Oldsmobile F-85 and 1961–1962 Pontiac Tempest and was the lightest mass-production V8 in the world.

The Buick version had a dry, undressed weight of 318 lb (144 kg) and the 1963 Skylark with optional four-barrel Rochester carburettor and 10:1 compression ratio produced 200 hp (150 kW) at 5,000 rpm. By the time Rover had made webbing modifications to strengthen the block, the engine was considerably heavier (over 170 kg). Some changes were made by MG-Rover and the engine found a long-lived niche in the British motor industry.

These cars were similar to those already being produced in significant volume by tuner Ken Costello. MG even contracted Costello to build them a prototype MGB GT V8. However, the powerful 180 bhp (134 kW) engine used by Costello for his conversions was replaced for production by MG with a more modestly tuned version producing only 137 bhp (102 kW) at 5,000 rpm. Nonetheless, 193 lb⋅ft (262 N⋅m) of torque helped it hit 60 mph (97 km/h) in 7.7 seconds and go on to a 125 mph (201 km/h) top speed. Fuel consumption was just under 20 mpg.

By virtue of its aluminium cylinder block and heads, the Rover V8 engine weighed approximately 40 pounds less than MG's iron four-cylinder. Unlike the MGC, the V8 that provided the MGB GT V8's increased power and torque did not require significant chassis changes nor sacrifice handling.

Both chrome and rubber-bumpered GT versions of the V8-powered MGB were produced by the factory with production ending in 1976.

MG never attempted to export the MGB GT V8 to the United States. It chose not to develop a left-hand-drive version of the MGB GT V8 although the Rover V8 engine was offered in US-bound Rover models. The P6 3500 was withdrawn after 1971 from the US and the Rover 3500 SD1 only introduced in 1980 (its engine equipped with power-sapping emissions equipment) so that during the lifetime of the MGB GT V8 the engine was not being built in a federal version. Abingdon built seven LHD models, sent them to America to achieve certification, and brought them back to the UK to be sold to mainland European countries.