This works was located north of Glengarnock itself and south of Kilbirnie Loch. It latterly produced flats and sections and 'Glengarnock' marked rails were a common sight.
Its iron works was opened by Alexander Cunninghame and James Merry in 1843 alongside the 1840 Glasgow, Paisley, Kilmarnock and Ayr Railway just north of Glengarnock station. There was a network of private line from the works to reach iron ore mines to the west (Glengarnock Blast Furnaces, Pitcon Railway) and south (Barkip Railway, Muirhouse and Barkip Railway, Hillhead Railway, South Portion (Barkip Railway)).
Connection to the main line was via two junctions Glengarnock Iron Siding to the north and Glengarnock Coal Siding closer to the station. The Glengarnock Iron Works were on the west side of the line with the slag road running to Kilbirnie Loch which was tipped into, slowly extending the south shore northwards.
The steel works was built to the west and north of the iron works in 1885. It was the only one of the Ayrshire iron works to become a steel works.
In 1889 the Barkip Railway was incorporated into the Lanarkshire and Ayrshire Railway and the approach to the works altered to approach the west end of the works, rather than the iron works. Access to the works was by reversal to reach Glengarnock Yard, to the west of Glengarnock [CR] station.
In 1905 the Kilbarchan Loop (Glasgow and South Western Railway) opened on the west side of the works, connection being close to Kilbirnie [2nd] station.
In 1978 the works was reduced to a rolling mill. It closed in 1985.