Nixon was born in New York City, New York, the daughter of Anne Knoll, an actress, and Walter Nixon, a radio journalist.Her first onscreen appearance was as an imposter on To Tell the Truth, where her mother worked. She began acting at age 12 as the object of a wealthy schoolmate's crush in The Seven Wishes of a Rich Kid, a 1979 ABC Afterschool Special. She made her feature debut co-starring with Kristy McNichol and Tatum O'Neal in Little Darlings (1980). She made her Broadway debut as the bratty Dinah Lord in a 1980 revival of The Philadelphia Story. Alternating between film, TV and stage she did projects like the 1982 ABC-movie My Body, My Child, the features Prince of the City (1981) and I Am the Cheese (1983) and the 1982 off-Broadway productions of John Guare's Lydie Breeze. In 1985 she appeared alongside Jeff Daniels in Lanford Wilson's Lemon Sky at Second Stage Theatre.