John Williams is an Australian scientist whose life work has been in the study of hydrology and the use of water in the landscape and farming, including land salinity.

[2] Williams is a founding member of the Wentworth Group of Concerned Scientists and advocated for a rational debate on Australia's water resources.

[3] He was Chief of the Division of Land and Water, CSIRO (Australia's premier government research organisation), in Canberra, when he retired in 2004.

[4][5][6] Williams is an emeritus professor and research associate at the Australian National University;[7] and a commentator on environmental matters.

[9] In February 2018, Williams was a co-author of an article in The Conversation and co-signatory of the Murray Darling Declaration along with other concerned scientists.