William Chadwell Mylne, FRS (6 April 1781 – 25 December 1863) was an English civil engineer and architect.

He was descended from a Scottish family of masons and architects, and was the second son of Robert Mylne (1733–1811), surveyor to the New River Company, and builder of the first Blackfriars Bridge in London.

Initially, William's elder brother Robert was intended to take over his father's business, but when Robert opted for a military career, William began to assist his father, surveying land for the Eau Brink Cut, on the River Great Ouse, in 1797.

[2] Mylne later designed the gothic St Mark's Church, Myddelton Square (1826–1828), and Clerkenwell Parochial Charity Schools (1828).

[2] Other architectural works include a card room at Stationers' Hall, London, Harpole Rectory in Northamptonshire (1826), and his own home, Flint House, Great Amwell (1842–1844).