Mirrlees, Bickerton & Day Ltd was established in Hazel Grove, Stockport, in 1908, by Charles Day. Day was the manager of Mirrlees, Watson & Co of Glasgow, where he had introduced diesel engines to the company's manufacturing range. The diesel engineering business increased rapidly, and Day was tasked with finding new premises to establish a facility solely for the manufacture of diesel engines. With the financial backing of Henry Neild Bickerton of the National Gas Engine Co, Day established the new company.

Between 1908 and 1914, Mirrlees, Bickerton & Day supplied diesel engines to the Royal Navy, the Merchant Navy, Manchester Docks, and power stations. The First World War saw the company develop an oil engine for use in tanks that allowed for the use of tar oil in place of fuel oil, which was difficult to import due to blockades.

In 1924, Mirrlees, Bickerton & Day developed the Simplex small semi-diesel engine for use in generating stations and flour mills. The following year saw the introduction of the Nobel engine used in railway workshops and generating stations. As well as developing new, lighter engines, the company also investigated the impact of increased revolution speeds on engine vibration.

In 1926, Mirrlees, Bickerton & Day amalgamated with Mirrlees, Watson & Co, with full incorporation happening in 1933.

During the Second World War, Mirrlees, Bickerton & Day concentrated on engine production for defence, supplying power for radar, radio-location, airfield and various lighting systems for the Air Ministry. The existing close relationship with the Royal Navy continued, with the company supplying engines for minesweepers, towing vessels and landing craft, auxiliary generating sets for shipboard use, and generating sets for naval bases and fleet air arm stations.

In 1944, Associated British Engineering acquired Mirrlees, Bickerton & Day, with Mirrlees, Watson & Co remaining a separate company under the new name Mirrlees Watson Co. Associated British Engineering subsequently transferred Mirrlees, Bickerton & Day to the Brush Group in 1949. From 1950, the company manufactured new types of engines, the J and the K type, and a new method of production known as Flow Production. This production technique was unique to Mirrlees, Bickerton & Day and, coupled with new tooling, a new works layout and the new engine types, made the company one of the most modern diesel engine manufacturers in the world.

In 1961, Hawker Siddeley acquired Associated British Engineering, including Mirrlees, Bickerton & Day. The same year, Mirrlees, Bickerton & Day merged with the National Gas and Oil Engine Co to form Mirrlees National Ltd, ending the name Mirrlees, Bickerton & Day. Mirrlees National Ltd became Mirrlees Blackstone in 1969, following its merger with Blackstone and Co.