Harrold was born in Tazewell, Virginia. She has appeared in a number of TV series, including The Rockford Files, MacGruder and Loud, The Bronx Zoo, I'll Fly Away, The Larry Sanders Show', and Mister Sterling. She attended Mills College, majoring in Drama.

She was Steve McQueen's leading lady in the screen legend's final film, The Hunter, and Arnold Schwarzenegger's leading lady in the action vehicle Raw Deal. She appeared in Nightwing (1979) and co-starred with Luciano Pavarotti in Yes, Giorgio (1982).

Harrold starred in 1981's Modern Romance, where she played the ex-girlfriend of Albert Brooks' character. The film received a limited release and ultimately grossed under $3 million domestically, but was well received by critics, with one reviewer commenting that the film was "not Brooks at his best, but still amusing".

In the 1985 release, Into the Night, an action / suspense film directed by John Landis, she had a supporting role opposite Paul Mazursky as his girlfriend. When a quartet of Middle Eastern thugs raid the beach house they share, her character is shockingly one of the few fatalities in this violent yet comedic film. The character is a trusted friend to Diana, played by lead Michelle Pfeiffer, the central character and courier of stolen gem stones, who is pursued with antic zeal throughout the film by the same four thugs in a manner reminiscent of the Keystone Kops.

She has also appeared in several TV movies, most notably the 1980 Bogie in which she played movie legend Lauren Bacall (reportedly against Bacall's wishes) and the 1988 HBO film Dead Solid Perfect in a leading role performance opposite Randy Quaid.

Harrold dated co-star Albert Brooks on the set of his film, Modern Romance. Since 1994, Harrold has been married to political analyst Lawrence O'Donnell, former aide to Daniel Patrick Moynihan, and former Staff Director for the Senate Finance Committee. He is currently an MSNBC political analyst. O'Donnell was an executive producer of the award-winning TV series The West Wing.

Harrold plays Helen Rowland in Desperate Housewives.