Slater served as an engineer and surveyor for the East Indian Railway (as reported in the Morning Post, Thursday 9 September 1847). Slater had already been in India for some time prior to 1847, and he accompanied the railway's chief engineer George Turnbull on many of his surveying excursions during 1850, helping him assess the best route for the line.

Slater drew at least three portraits, two of which are in the National Railway Museum Collection (object number 2017-7098). In his autobiography Turnbull wrote of acquiring ‘Slater’s likeness’ of a ‘Captain Boscawen’, adding that ‘it is a very good’ likeness (July 1850). The whereabouts of this portrait is no longer known.

In 1851 Turnbull noted that Slater was exhibiting symptoms of pulmonary disease. Turnbull stayed at Slater’s residence in Howrah on 7 January 1852, which is perhaps when these drawings were made. Soon after, Slater’s symptoms worsened, and he sailed for London on 24 January on a leave of absence. He died shortly after arriving. The two drawings in the NRM Collection, dated 1852, are perhaps the final two he made.