Robert Sinclair was born in 1817, and entered private boarding school before being apprenticed to shipbuilders. After his apprenticeship, he worked for Robert Stephenson, followed by the Grand Junction Railway, and then the Paris & Rouen Railway. After this experience, he became the Caledonian Railway's first Locomotive Superintendent in 1848.
In 1856, Sinclair moved to the Great Eastern Railway (GER) where he was responsible for the early development of the GER's Stratford Works. At the GER, Sinclair introduced the GER's stovepipe chimney and a very protective design of locomotive cab. Sinclair also promoted a high level of standardisation amongst his locomotive designs.
Sinclair resigned in 1865, and set himself up as a consulting engineer. As such, he introduced a fast 2-4-2 locomotive on the Great Luxemburg Railway, and an outside cylinder 2-4-0 design for the East Indian Railway. He also adapted the Luxembourg 2-4-2 design into a 2-4-2T for the GER's commuter services.
Sinclair died in 1898.