Beginning her career as a child actress, she rose to fame in 1976 with her portrayal of teenaged daughter Letitia "Buddy" Lawrence in the TV drama Family for which she won two Emmy Awards.

Subsequent roles included Angel in the film Little Darlings, Polly in Only When I Laugh, and Barbara Weston in the TV sitcom Empty Nest.

Her father was a carpenter and her mother worked odd jobs to support the family, including as a secretary, cosmetics salesperson, and movie extra.

[10] Later in 1980, she appeared with Dennis Quaid and Mark Hamill in The Night the Lights Went Out in Georgia, for which she received a six-figure salary—unprecedented for a teenager.

[citation needed] The same year, she suffered an emotional breakdown while playing the lead role in the comedy-drama Just the Way You Are that was being filmed in France.

She did not return to the production after Christmas to finish the movie; filming had to be interrupted for a year while McNichol recovered.

In 1986, McNichol appeared in Women of Valor, a TV movie about American nurses in a World War II Japanese POW camp.

So many fans are disappointed that I'm not currently acting; however, some may not realize that the process I'm in at this time is necessary and vital for my personal happiness and well-being.

After her retirement, McNichol taught acting at a private school in Los Angeles and devoted much of her time to charity work.

[14] In 2012, McNichol ended years of speculation when she revealed that she is a lesbian and has lived with her partner Martie Allen since the early 1990s.