He was raised in Cornwall and studied theology at King's College, London University; his first published book, A Church Renascent (1951), is a study of left-wing French Catholicism. He immigrated to North America and moved to Vancouver in 1962, where he lived until his death.

Watmough described his literary project as "a fictional autobiography of Davey Bryant, a twentieth-century man who happens to be an author, an immigrant and a homosexual." He wrote 11 novels and short story collections that evoke Bryant's recollections of the past and detail his picaresque journey from childhood in England to the west coast of Canada. The works include Ashes for Easter and Other Monodramas (1972), No More Into the Garden (1978), The Connecticut Countess (1984), Fury (1984), Thy Mother's Glass (1992), and The Time of Kingfishers (1994). Throughout these works, Bryant searches for significant human contact and struggles with the homophobic society that surrounds him, his own painful self-consciousness, and the deaths of family and friends. Bryant functions as an alter-ego through which the author explores human relationships, sexual identities and the converging of the political and the personal with irony, candour and compassion.

Watmough also wrote plays, three of which are collected in Names for the Numbered Years (1967). The Unlikely Pioneer (1986) is a study of Irving Guttman's impact on the development of opera in the Canadian West. Hunting With Diana (1996) was inspired by his knowledge of Greek myths and finds Bryant surfing the Internet.