She had a regular role in the BBC drama series "The Brothers" (1975–1976) as Jane Maxwell, and in the early 1980s, O'Mara starred in the BBC soap opera "Triangle" (1981–1982), sometimes counted among the worst television series ever made. She played the villainous Rani in "Doctor Who" in two serials, "The Mark of the Rani" (1985) and "Time and the Rani" (1987), and also in the "Doctor Who" 30th anniversary spoof "Dimensions in Time" (1993), part of the "Children in Need" charity event.