Born in Burbank, California, USA on October 18, 1960, Erin Moran was the youngest daughter of Sharon and Edward Moran, who have five other children. She attended Walter Reed Junior High School for one year and North Hollywood High School for another year. Her first professional acting job was in a TV commercial. She played Richie Cunningham's baby sister, Joanie Cunningham, on ABC's Happy Days (1974); however, this was not Erin's first major TV series. She was a regular on the series, Daktari (1966). She has also made guest appearances on TV series such as The Waltons (1972), Family Affair (1966), My Three Sons (1960), The Courtship of Eddie's Father (1969), Gunsmoke (1955), The Smith Family (1971), and The F.B.I. (1965).

Erin Moran has worked on feature films with Debbie Reynolds in How Sweet It Is! (1968), with Godfrey Cambridge in Watermelon Man (1970), and with Wayne Newton in 80 Steps to Jonah (1969).

Like many other child actors, Erin had difficulty finding roles as an adult. Following the cancellation of Happy Days (1974) in 1984, she made occasional guest appearances on scripted and reality shows. She eventually moved away from Hollywood after her home was foreclosed on.

On April 22, 2017, she died in Corydon, Indiana, where she had been living with her husband of 23 years; she was 56 years old.