McNichol began her film career in 1977, in Black Sunday, but her scenes were cut during editing. In 1978, she starred with Burt Reynolds in the comedy The End. In 1980, she played the leading role in the hit coming of age movie Little Darlings, which co-starred Tatum O'Neal, Matt Dillon, and Cynthia Nixon. Her performance was acclaimed by many reviewers, including those who disliked the film itself.