James Henry Greathead (6 August 1844 - 21 October1896) was an engineer renowned for his work on the underground railway networks of London.

Born in Grahamstown, South Africa he moved to Britain in 1859 to continue his education in civil engineering. In 1864 he began working with Peter W. Barlow and then spent time (around 1867) as assistant engineer on the Midland Railway between Bedford and London (working with Barlow's brother, William Henry Barlow).

Soon after, in 1869, he rejoined Barlow and they began work on designs for the Tower Subway, a tunnel under the river Thames in central London. This began a long fascination with the challenges of tunnelling through soft, waterlogged soil. Today Greathead is particularly remembered for his pioneering work in relation to tunnelling shield techniques, in which he greatly improved the shield developed by Marc Isambard Brunel in 1818 for the construction of the Thames Tunnel. He patented many of his improvements including use of compressed air and forward propulsion by hydraulic jacks, both of which are now standard features of tunnel construction.

Greathead was Chief Engineer on the City and South London Railway (now part of the Northern Line, opened in 1890), and, shortly before his death in Streatham, London , began work on the Central Line (opened 1900) with Sir Benjamin Baker. He was also a consultant in relation to the construction of the Blackwall Tunnel and the Waterloo & City Line, both completed after his death.

An English Heritage blue plaque marks his home in Barnes, south-west London, 3 St Mary's Grove, where he lived between 1885 and 1889.