On Broadway, she was a cast member of the 1975 revival of Cat on a Hot Tin Roof, as well as The Rothschilds, and Boccaccio. Off-Broadway, she worked for the Public Theater and the American Shakespeare Festival.
McWilliams played the role of Marcy Hill on the sitcom Benson, and played Janet Mason for six seasons on the CBS soap opera Guiding Light. Among her film and television credits are Mermaids, White Water Summer, Highway Time, Soap, and Beverly Hills, 90210.
She is survived by her son Sean Douglas and her sisters, Patti McWilliams, Norma Liedtke, and Kelly-Jo Dvareckas.