An author and an academic, Kiernan was a student of Xavier College, and later completed a Bachler of Arts, Master of Arts, and a Diploma of Education at Melbourne University.
In the late 1960s Kiernan was appointed as a lecturer in Literature at the Swinburne College of Technology in Melbourne. He left there in 1972 to join the English Department of the University of Sydney as a lecturer, teaching American and Australian literature. In 1987, he was appointed as an Associate Professor of English at the University of Sydney. Kiernan was also a lecturer for the Australia Council and the Department of Foreign Affairs at universities in France, Italy, Denmark and England. In 1976, he was Visiting Fellow in American Studies at Yale University.
As well as his work as a university teacher, Kiernan wrote and edited books on Australian fiction, poetry and drama and contributed articles and reviews to a number of newspapers and journals.
He was a founding member, and for many years President, of the Association for the Study of Australian Literature (ASAL), and was the Australian representative for the American Association of Australian Studies, as well as a long-time committee member of the NSW Writers' Centre.
He was the cousin of Desmond O'Grady.
Sources include: National Library of Australia finding aid, Michael Wilding obituary of Keirnan (email).