This very long established engineering company was founded in 1840 by Andrew Barclay and Thomas McCulloch who had a workshop in Portland Street, Kilmarnock. McCulloch left the business in 1842 and Barclay moved to a new works in West Langland Street during 1844; this has become the site of the famous Caledonia Works. 1888 saw Andrew Barclay Sons & Co. Ltd merge with Barclays & Co., a company run by other members of the same family.

The first steam locomotive by Andrew Barclay was built in 1859, when the first of many 0-4-0 saddle tanks appeared; and the last built was in 1962 when No. 2377, an 0-6-2T, was constructed for an Indonesion customer. Barclays were an early competitor in the diesel locomotive field, building their first in 1916, although they did not produce internal combustion engined machines with any regularity before 1935. This form of traction is now their staple trade and the works at Kilmarnock are still in production.

Andrew Barclay was also a leader in the field of fireless locomotives and they produced more of this type than any other British manufacturer, but the company is best known for its simple, robust 0-4-0 and 0-6-0 saddle tanks.

Today Andrew Barclay is the only locomotive builder in Scotland, having become part of the Hunslet Group of companies in 1972, having brought out Fowler's railway business in 1968.

Examples at Quainton