Marion Griffith Eames was born in Birkenhead, England, to a Welsh family. When she was four years old, they moved to Dolgellau in northwest Wales, where she attended Dr. Williams's School. She went to work as a librarian, first at the County Library in Dolgellau and then at the University College of Wales, Aberystwyth. A few years later, she tried journalism as editor of the weekly newspaper Y Dydd. She was a talented harpist, and was able to fulfill a longstanding dream when she entered the Guildhall School of Music, London. In 1955, she married Griffith Williams, a journalist. They both obtained jobs in Cardiff, Marion as a radio producer with the BBC, a position she held until retirement in 1980. She was also an organizer for Plaid Cymru, the Welsh nationalist party. She established herself as a writer in Welsh of historical novels, including her best-known work, Y Stafell Ddirgel (The Secret Room, 1969), later adapted into a television drama by the BBC, and its sequel Y Rhandir Mwyn (Fair Wilderness (1972). She also wrote books for children and published her autobiography in 1995.