William Mark Nixon (31 May 1859 – 5 June 1931) was an Australian architect active at the end of the 19th century and the first quarter of the 20th century. His work encompassed the styles of the Federation Bungalow in domestic design and Federation Free Classical in civic and commercial design. He was active in local government and was President of Hornsby Shire and an Alderman in the Municipality of Ashfield.