Born in 1941, Marshall graduated with an MA (Hons) from the University of Canterbury, and went on to practice as a teacher for over 25 years. Over the course of his career he has written or edited 30 books, and his numerous awards for fiction include the New Zealand Literary Fund Scholarship in Letters, fellowships at Otago and Canterbury universities, and the Katherine Mansfield Memorial Fellowship in Menton, France. In 2000 his novel Harlequin Rex won the Montana New Zealand Book Awards Deutz Medal for Fiction.

Also in 2000, Marshall became an Officer of the New Zealand Order of Merit (ONZM) for services to literature, and in 2012 was made a Companion of the New Zealand Order of Merit (CNZM). In 2013 he received the Prime Minister's Award for Literary Achievement in Fiction.

Although he was born in Te Kuiti, the majority of Marshall's life has been spent in the South Island towns of Blenheim, Oamaru and Timaru, and a feeling for place permeates his work. He has compiled two anthologies, Essential New Zealand Short Stories and Best New Zealand Fiction #6, and collaborated with painter Grahame Sydney and poet Brian Turner on Timeless Land, an appreciation of the landscapes of the Central South Island.

Writer and academic Vincent O’Sullivan has said of Marshall that ‘nobody tells our [New Zealand] stories better’.