The Austin 1800 S Mk II was a sportier version of the Mk II series, offering enhanced performance and subtle styling upgrades. Introduced in the late 1960s, it was powered by a more potent version of the 1.8-liter B-series engine, featuring twin SU carburetors that increased power output compared to the standard model. This improvement provided a livelier driving experience while maintaining the comfort and practicality of the original design.

Externally, the 1800 S Mk II retained the distinctive shape of the Mk II series but included minor styling revisions such as a redesigned grille and improved lighting. Inside, it featured an upgraded interior with better trim materials and a revised dashboard layout. The Hydrolastic suspension, a hallmark of the model, continued to provide a smooth and composed ride, making it a comfortable yet capable vehicle for long-distance travel.

The Austin 1800 S Mk II was appreciated for its balance between practicality and performance, offering more power without sacrificing reliability. It remained a solid choice for those who wanted a spacious and well-engineered car with a bit more enthusiasm on the road. Production continued until the early 1970s, when the 1800 range was eventually succeeded by the Austin 2200 and other newer models.