Born in Boston, Massachusetts, daughter of Muriel Descoteaux Twomey and Harry F. Twomey, Jr. of Gladwyne, Pennsylvania. She had a brother, John Twomey. John is married to Maria S. Chan. Twomey earned critical acclaim for her performance in the 1980 play Nuts, for which she won the Theatre World Award and was nominated for the Tony Award for Best Performance by a Leading Actress in a Play. Her additional Broadway credits include To Grandmother's House We Go (1981) and Orpheus Descending (1989). Off-Broadway she appeared in Vieux Carré (1983), 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.
Twomey had recurring roles in the 1993 season of L.A. Law and the 2000-01 season of Third Watch. She has made guest appearances on Shannon (1981 TV series), The Cosby Show, 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.
