John O'Brian is a Canadian art historian, writer, and curator. He is best known for his books on modern art, including Clement Greenberg: The Collected Essays and Criticism, one of The New York Times "Notable Books of the Year" in 1986, and for his exhibitions on nuclear photography, such as Camera Atomica, organized for the Art Gallery of Ontario in 2015—the first comprehensive exhibition on postwar nuclear photography. From 1987 to 2017, he taught at the University of British Columbia, Vancouver, where he held the Brenda & David McLean Chair in Canadian Studies and was an associate of the Peter Wall Institute for Advanced Studies. O'Brian has been a critic of reactionary cultural policies since the start of the Culture Wars in the 1980s. Martha Langford writes that O’Brian has had “nine lives in the visual arts, from Greenberg’s and Canadian Modernism’s explicator to the Western photographic turn via wilderness and the nuclear winter of global discontent. O’Brian writes very much from the middle of things.”