Margaret Ellis Millar (née Sturm) (February 5, 1915 – March 26, 1994) was an American-Canadian mystery and suspense writer.

Born in Berlin, Ontario, (the city would change its name to Kitchener in 1916), she was educated at the Kitchener-Waterloo Collegiate Institute and the University of Toronto. She moved to the United States after marrying Kenneth Millar (better known under the pen name Ross Macdonald). They resided for decades in the city of Santa Barbara, which was often used as a locale in her later novels under the pseudonyms of San Felice or Santa Felicia. The Millars had a daughter who died in 1970.