An effervescent, square-jawed blonde performer, Plimpton made her mark playing the estranged daughter of Tommy Lee Jones in "The River Rat" (1984) and gave a fine performance as the girlfriend of River Phoenix in Sidney Lumet's "Running on Empty" (1988). Her early roles as appealing tomboys in such films as "The Goonies" (1985) and "The Mosquito Coast" (1986) were reminiscent of Jodie Foster's persona of the 1970s. After "Running on Empty", the casually attractive Plimpton played the archetypal adolescent daughter with a rebellious strain in "Parenthood" (1989) and in "Samantha" (1992). She graduated to adult parts with Alan Rudolph's "Mrs. Parker and the Vicious Circle" (1994), playing the supporting role of noted wit Jane Grant. The film marked the first pairing of Plimpton and her father Keith Carradine, who appeared in a cameo as Will Rogers.

Plimpton has continued to land interesting roles that challenge her abilities. Ted Demme cast her as Michael Rapaport's fed-up girlfriend in "Beautiful Girls" while Mary Harron teamed her with Lili Taylor in "I Shot Andy Warhol" (both 1996). Perhaps Plimpton's most challenging role to date was Ainsley in Tim Blake Nelson's "Eye of God" (1997). The actress proved most effective as a trusting, love-starved young woman whose relationship with an ex-con forms the central story in the independent film. She followed with a turn in the romantic comedy-drama "Music From Another Room" (1998). In addition to her film work, Plimpton has frequently appeared on stage, including in Eric Bogosian's 1994 Off-Broadway play "subUrbia" and the 1996 Steppenwolf Theatre production of "The Libertine" opposite John Malkovich. More recently, she has appeared in the Showtime TV-movie "The Defenders: Payback" (1997), the first in a series of longforms based on the old TV show. Plimpton was cast as M.J. Preston, a former prosecutor and the granddaughter of Lawrence Preston (E.G. Marshall) who joins her grandfather's law firm.