[1] Mackay made her stage debut at the American Shakespeare Festival, Stratford, Connecticut, in 1970.
She appeared in many productions at The Cleveland Play House from 1975 to 1978, including Man and Superman, Dark at the Top of the Stairs, Relatively Speaking, Of Mice and Men, Great Expectations, and Little Foxes.
Mackay starred in Night, Mother with Katherine Helmond in early 1998 at the Orpheum Theatre in Foxboro, Massachusetts for which she won an Elliot Norton Award.
later that year, she starred in A View From The Roof at Barrington Stage Company and the Orpheum Theatre.
[5] Mackay's feature film credits include Malcolm X (1992), Marvin's Room (1996), and One True Thing (1998).