The Austin FX4 is a hackney carriage (taxicab) that was produced from 1958 until 1997. It was sold by Austin from 1958 until 1982. Only 75,000 cars were ever built and few exist in the US. The Austin FX4 cab tootled around London, England as the successor to the Austin FX3, which in its day, was London's most widely used taxi. Most taxis were fitted with the Austin diesel engine, though a rare few had the gasoline 2.2L engine. The FX4 was the first taxi in London to have four doors.

The first model of FX4 was fitted with a 2178 cc Austin diesel engine and a Borg-Warner automatic transmission. In 1961, the manual transmission from the Austin Gipsy was added as an option. From 1962, the Austin 2199 cc petrol engine was available. However, almost all FX4 taxis were fitted with a Diesel engine.

The original Austin design had a small rear light cluster and roof-mounted turn indicators (commonly known as "bunny ears"). On the revised model, the rear wings were modified to accept the taillights and turn indicators from the MkII Austin 1100/1300. Front indicators were also provided below the headlights and repeater indicators fitted to the front wings and "bunny ears" were abandoned.