Dwyer is best known for appearing in several horror films distributed by American International Pictures in the late 1960s and early 1970s, most notably Michael Reeves' Witchfinder General (1968), starring Vincent Price.

She also appeared in The Oblong Box (1969) and Cry of the Banshee (1970), both again featuring Price, as well as Robert Fuest's Wuthering Heights (1970). Banshee was her final feature film appearance. Her many television roles included The Prisoner, The Avengers, Hadleigh and Van der Valk. Her last TV appearance was in a 1976 episode of Space: 1999.

In 1973 Dwyer set up the talent agency Duncan Heath Associates with her then husband-to-be Duncan Heath, now the co-chairman of the Independent Talent Group Ltd. In a 2002 interview in the Financial Times, Heath said of Dwyer "She introduced me to a lot of people - if it wasn't for her it wouldn't have happened."

Dwyer married talent agent Duncan Heath in 1974; they divorced in 1989. They have two children, Laura and Daniel. Laura Heath founded and runs the Hope-Martin Animal Foundation in Barbados.

She began a career as a Producer in the mid-1980s under her married name Hilary Heath. She is credited as either Producer or Executive Producer for several films, including feature films Criminal Law (1989) and Nil by Mouth (1997) as well as TV-remakes of Daphne du Maurier's Rebecca (1997) and Tennessee Williams's The Roman Spring of Mrs. Stone (2003).