While its predecessors were very closely based on the "Bullnose" Morris Oxford, the MG 18/80 was the first model in which the factory had designed the chassis itself, and was the first car to have the typical MG grille with vertical standing slats and vertical center bar and higher set headlights. It was initially known as the 'MG Six'.
The MG 18/80 derived from the Morris Light Six/ Morris Six, for which Cecil Kimber had MG build a stronger chassis.
The Mark I and Mark II were available in a variety of body styles, two- and four-door, two- and four-seater and both closed and touring cars. The Mark I was built from 1928 to 1931, to a total of 501 examples. From 1929 onwards, the Mark II was offered in parallel, with 236 built.
The cars were equipped with six-cylinder inline engines with chain-driven overhead camshafts. They were of 2468 cc displacement and had a double carburetor with only one float chamber. The power was about 60 bhp (44 kW), giving a top speed of 80 mph (128 km/h), as indicated by the '80' in the product designation 18/80.
The Mark III was referred to variously as '18/80 Tigress' and the '18/100' and was a racing version launched in 1930. Only five vehicles were produced. This version had dry sump lubrication and its engine was rated at 80 hp (59 kW).
There was no direct successor. Only in 1936 would the MG VA, the next large MG, come on the market.