William James Hewlett (1876 – 1921) was a British trade unionist and socialist activist.
He became interested in syndicalism, and during the Cambrian Combine dispute of 1911, he worked with Noah Ablett, Will Hay and Bill Mainwaring who formed the Unofficial Reform Committee.
He also led the reformation of the SWSS as the "South Wales Communist Council", and then participated in the formation of the Communist Party of Great Britain, serving on its provisional executive committee.
He went on a visit to coal miners in Tula, but died in an accident on an experimental high-speed railcar during the trip.
Hewlett, and the other victims, lay in state in the Great Hall of Columns, and he was then buried near the Kremlin Wall.