Her additional Broadway credits include To Grandmother's House We Go (1981) and Tennessee Williams' Orpheus Descending (1989).
Off-Broadway she appeared in Vieux Carré (1983), also by Williams, which garnered her a Drama Desk Award nomination for Outstanding Featured Actress in a Play, and The Vampires (1984).
Twomey's feature film credits include Deadly Friend (1986), Last Rites (1988), The Scout (1994), Picture Perfect (1997), and The Confession (1999).
She has made guest appearances on Shannon, The Cosby Show, The Twilight Zone, Magnum, P.I., Seinfeld, Spin City, Law & Order, Law & Order: Special Victims Unit, and Law & Order: Criminal Intent, and had a featured role in the 1998 television remake of Rear Window starring Christopher Reeve and Daryl Hannah.
Twomey has narrated several audiobooks, including works by Dean Koontz, Joyce Carol Oates, Tracy Chevalier, and M. T. Anderson.