The first new locomotive was built at the works in 1864. Though the railway had amalgamated with the North Eastern Railway in 1863, it continued to build its own designs for a number of years. In 1877 the first North Eastern designs appeared. Additionally works where constructed west of the S&DR railway in the Stooperdale area of Darlington. Grandiose offices for the NER were also constructed in the Stooperdale area in 1911, to the design of William Bell. The offices were used by NER chief mechanical engineerVincent Raven until 1917. In 1914 a class of NER Bo-Bo electric locomotives was built at the works to run between Shildon and Newport. Ten of these 1500 volt direct current locomotives were completed. Sir Vincent Raven designed the NER Class T2 0-8-0 freight locomotive in 1913, and by 1921 the works had built 120 of the engines, which were later designated Q6 by the LNER. The heavier and more powerful Raven NER Class T3 0-8-0 followed in 1919, 15 engines being completed by 1924.
LNER period
Under the LNER it continued to play a major role, producing a new engine each week, with Gresley's K3 class 2-6-0 appearing in 1924. Both the class V2 and A1 express locomotives were also built. By 1927 the works was the town's largest employer. Darlington works built six LNER Class K4 2-6-0 locomotives in 1937/38 for operation on the West Highland Line. No. 3442 The Great Marquess has been preserved in full working order and in 2009 was still hauling special steam trains on the UKmain line network.
After nationalisation, Darlington built both steam and diesel locomotives, including BR standard class 2. The equivalent of the NER Class E10-6-0tank locomotive had been built, virtually unchanged since 1898. In 1954 during the modernisation of British Railways the works was enlarged and had grown to cover over, but in 1962 the BR Workshops Division was formed and, with rationalisation, the works was run down and closed in 1966. The land of the Stooperdale part of the works was sold to Whessoe in 1962.
Current use of the site
The site since about 1979/80, is occupied by the Morrisons supermarket, and the adjacent Bowls Hall, with the original clock which was restored, was re-erected by contractors Fairclough Building Ltd onto the east wall of the supermarket overhanging North Road. The Stooperdale offices were grade II listed in 2001.