Born in Minneapolis, Minn., Neill initially planned to become a journalist. But during a trip to California as a teenager, she caught the eye of Bing Crosby while working as a singer at his racetrack, and he introduced her to his brother, a theater agent.
Neill already had a substantial acting resume under her belt (though mostly small roles) when she was cast as Lois Lane in 1948 for 15 episodes of the serialized movie Superman, opposite Kirk Alyn in the title role. When the television adaptation Adventures of Superman was being developed in the early 1950s, Phyllis Coates was tapped to play Lois Lane opposite George Reeves, but Neill replaced her after one season, until the show ended in 1958. Reeves committed suicide the following year.
After Adventures of Superman, Neill quit acting and began a career in public relations, working in the TV department at United Artists. In the 1970s, she made several appearances at Superman fan conventions, and also had cameos in 1978's Superman and other offshoots, including the TV series The Adventures of Superboy and 2006's Superman Returns.
Neill was married three times - her first marriage was annulled and her subsequent two both ended in divorce. She has no survivors.