Wainwright began his career at the age of 14, working at the carriage shops of the Midland Railway, under T. G. Clayton. in 1882 he moved to South Eastern Railway, where he worked with his father. In 1889 he became an inspector, and in 1890 he was promoted to works manager, Carriage & Wagon department. By 1899 he had been appointed to the position of chief locomotive engineer and Carriage & Wagon superintendant on the formation of South Eastern & Chatham Railway. He was forced to retire in 1913, on grounds of ill health.