Born May 24, 1933 in Toronto, Ontario, to teacher parents Frederick Searle and Mary Elizabeth (Fletcher) Passmore. She grew up in Port Arthur, Brantford, Galt, Hamilton and Sarnia.
Engel was educated at Sarnia Collegiate Institute & Technical School, Sarnia, Ontario, McMaster University (B.A. in Language Studies 1955) Hamilton, Ontario, McGill University (M.A. in Canadian Literature 1957) Montreal, Quebec and studied on a Rotary Foundation Scholarship at the Université d’Aix-Marseille (French Literature 1960-61), Aix-en Provence, France. At McGill University she wrote her Master’s thesis on the English Canadian novel, under the supervision of Hugh MacLennan.
She taught briefly at The Study (1957–58) (Westmount, Montreal, QC), McGill University and University of Montana-Missoula (Missoula, Montana) and St. John’s School (Nicosia, Cyprus).
She met Howard Engel, a mystery novel writer and Canadian Broadcasting Corporation (CBC) radio producer in Canada, and married him in England in 1962. They returned to Toronto, ON in 1964. She began to raise a family, twin children, William Lucas Passmore and Charlotte Helen Arabella, and to pursue a writing career. Marian and Howard separated in 1975 and divorced in 1977.
Engel was writer-in-residence at the University of Alberta (1977–1978) and at the University of Toronto (1980–1982).
Engel died of cancer in Toronto on February 16, 1985.