In steam days the depot (behind Ninian Park Road)was called Cardiff Canton and its shed code was 86C. It was built in 1882 as the main maintenance base for the South Wales Railway and the major Welsh engineering base for the Great Western Railway(GWR). After nationalisation in 1948 it was a heavy overhaul base for British Railways.
Cardiff Canton was opened in June 1882 as a six road, 240-foot (73 m)-long shed, built to replace Long Dyke, 1.5 miles (2.4 km) east of Cardiff General station. The GWR enlarged the depot in 1897 with a 55 ft (17 m)-diameter turntable installed in a square locomotive shed with 28 roads radiating of off the turntable. In 1925 the GWR added a locomotive repair and lifting shed and a new coaling stage. In 1931 the original 55 ft (17 m)-turntable was removed and replaced by a larger 65 ft (20 m)-diameter one at the west end of the yard. At this time, around the peak of GWR operation, the depot had allocated 50 main line passenger locomotives, 40 heavy goods/ mineral locomotives and 30 smaller local passenger/goods and shunting locomotives. Steam traction at the depot ceased on 8 September 1962.
In the winter of 1962–63, Kyle Stewart contracted to build for British Railways a new £1,324,000 complex on a 30-acre (12 ha) site. Lord Brecon Minister of State for Welsh Affairs, opened the new depot on 18 September 1964
The original allocation was 360 locomotives for major maintenance, 197 for normal maintenance and 62 shunting locomotives. Employed were 40 managerial and supervisory staff, 31 clerical staff, 382 maintenance staff and 55 unskilled staff.