Born Sierra Ditson Moselle, in San Francisco, she attended Tamalpais High School in Mill Valley, California, graduating in 1998.

[3] In 2010 Moselle was walking around New York City, where she worked and lived, when she was struck by six brothers with an unusual appearance.

She began filming them and after a year learned that they had spent the majority of their lives stuck in a small four bedroom apartment due to their abusive father's paranoia of the outside world.

Moselle, who had been collaborating with teenage skater girls she had met in a park, decided to film them for her short That One Day.

[8] In 2020, Moselle served as writer, director, and executive producer of Betty, an HBO series based upon Skate Kitchen.