[1] Marion was born in Birkenhead, Cheshire, of Welsh parents – William Griffith Eames (1885–1959) and his wife Gwladys Mary (née Jones) (1891–1979) – but she was brought up from the age of four at Dolgellau, Merionethshire (Sir Feirionnydd), where she attended Dr Williams' School.
A talented musician, who played the harp and the piano, she graduated from the Guildhall School of Music and Drama in London.
Marion worked as a librarian in Dolgellau, then at Aberystwyth University, before becoming a radio producer with the BBC in Cardiff from 1955 to 1980.
In 1955 she married the Quaker journalist Griffith Williams, with whom she moved to Pimlico, then back to Cardiff.
Her best-known work of fiction is the historical novel Y Stafell Ddirgel (1969), which was translated into English by Margaret Phillips as The Secret Room (1975).