Quinn L. Cummings was born on August 13, 1967, in Los Angeles, California. Her father, Sumner, was a businessman who died when she was still a child. Her mother, Jan, was a bookkeeper.

Quinn Cummings began her career after being discovered by cinematographer James Wong Howe. She soon began landing roles in numerous television commercials, eventually winning the role of Marsha Mason’s daughter, Lucy McFadden, in the 1977 film The Goodbye Girl. Cummings’ performance was nominated for an Academy Award for Best Supporting Actress and a Golden Globe Award for Best Supporting Actress – Motion Picture. In 1978, Cummings had a recurring role on the drama series Family. In 1985, Cummings appeared in the short-lived ABC sitcom Hail to the Chief as the daughter of the first female president of the United States, played by Patty Duke. During the late 1980s, Cummings acted occasionally and worked as a casting agent. She quit acting because she was not comfortable living her life in the public eye. She attended UCLA for two years and had a stint recruiting writers to publish short stories online. Her last acting role was a 1991 episode of Blossom.

In 2000, Cummings gave birth to a daughter, Anneke DiPietro, by her partner Donald DiPietro.

In February 2005, Cummings started a blog, The QC Report, which discussed the ironies of modern life from the point of view of a career mother in her 30s. Cummings’ first book, Notes From The Underwire: Adventures from My Awkward and Lovely Life was published in July 2009. Her second book, The Year of Learning Dangerously, which explores the current state of home schooling in America, was published by Perigee Books in August 2012. Pet Sounds, a collection of humorous stories relating to animals and pet ownership was released in the summer of 2013. In 2019, she launched a podcast: “Quinn Cummings Gives Bad Advice” in which she responds to listener questions on any advice topic, highlighting the fact that she has no particular knowledge or expertise in the subject being raised.

Inspired by the birth of her daughter, Cummings created the HipHugger, a sling-type device for carrying a baby. She was the president of the HipHugger company before selling it in 2006.