Thea King was born in Hitchin, Hertfordshire, the daughter of Henry Walter Mayer King, the manager of a family engineering business, George. W. King Ltd., based in Hitchin then Stevenage, Hertfordshire, and his wife, Dorothea (née Hass). She was educated at Bedford High School and won a scholarship to the Royal College of Music where she studied the piano with Arthur Alexander and the clarinet with Frederick Thurston. In January 1953 she married Frederick Thurston but he died from lung cancer in December of the same year. She never remarried.