Born in Ottawa, Ontario, and raised in Nova Scotia, Gray obtained a B.A. at Mount Allison University, and an M.A. at the University of British Columbia. While attending the latter, he founded Tamahnous Theatre , and served as its director from 1971 to 1974. He then joined Theatre Passe Muraille in Toronto, Ontario, where he began writing and composing for the stage. His first musical was "18 Wheels," about truck drivers .

In 1978, with Eric Peterson, he wrote and composed Billy Bishop Goes to War , which appeared on Broadway in New York City in 1980, produced by Mike Nichols, and in London's West End. It has since been performed in over 150 independent productions in Canada and the United States. The play appeared on television in a BBC-CBC co-production, and in a German version, Billy Bishop Steig Auf. Billy Bishop Goes to War was the winner of the Los Angeles Drama Critics Award in 1981, the Governor General's Award for Drama, and the 1982 Floyd S. Chalmers Canadian Play Award.

Gray has written and composed six other musicals including 18 Wheels, Rock and Roll, Don Messer's Jubilee, Health, and Amelia. Rock and Roll won a Dora Mavor Moore Award in 1982, and became an award-winning feature video entitled King of Friday Night.

Gray's most recent musical is TheTree. TheTower. TheFlood , three Bible stories for the age of information, commissioned by CBC Radio Drama.

In the late 1990s, Gray became a newspaper columnist, contributing weekly pieces on cultural politics to the Vancouver Sun and the Globe and Mail. In the early 2000s he contributed a column to Western Living Magazine called "O For The Love Of Dog," in which he wrote about his dog Gus.

Around that time he abandoned the theatre in favor of the novel - in a series of thrillers set in post-modern Vancouver, mid-19th century England and the USA before the Civil War. As with "Billy Bishop Goes To War," Gray casts an ironic contemporary eye on imagined historical events.

He is the recipient of a Golden Globe, and the Governor General's Medal. In 2000, he was made an Officer of the Order of Canada for "his contribution to Canada's cultural landscape". He holds honorary doctorate from Dalhousie University and Mount Allison University.

John Gray lives in Vancouver, British Columbia with his wife Beverlee. They have two sons, Zachary (a musician and actor) and Ezra.