Naomi Grossman was born in Denver, Colorado. In her early life, she performed in community theatre shows. After attending high school in Argentina, she attended and graduated from Northwestern University with a theatre major, as the only university she applied to.
Naomi was a member of improvisational and sketch comedy troupe The Groundlings in Los Angeles, California, and wanted to ultimately perform on Saturday Night Live. When the group cut ties with her, she began teaching the Spanish language and separating herself from her acting career. She also writes and produces and has cited Lily Tomlin, Tracy Ullman, Gilda Radner and Carol Burnett as inspirations.
Grossman began her career in 1990 with minor television roles, along with commercial and theatre appearances. Not knowing what role she was auditioning for, Grossman sent in an audition for American Horror Story: Asylum in mid-2012 and was cast in soon after as Pepper, a microcephalic; the season premiered later that year on October 17. In preparation for the role, she shaved her head bald.
In 2014, it was revealed that Grossman would return to the series in its fourth season, American Horror Story: Freak Show, reprising her role as Pepper from the second season, making her the first to play the same role in two different seasons of the show. She spoke of her casting in the fourth season saying that reprising her role was "the last thing from [her] mind" since it had never been done before.