After beginning a career as a child model and actress in television commercials, Arngrim rose to fame as a child star in 1974, portraying the role of Nellie Oleson on the NBC television series Little House on the Prairie. She originally auditioned for the role of Laura Ingalls and, later, Mary Ingalls, but was instead cast in the role of antagonist Nellie Oleson. Arngrim would play the role of Nellie for seven seasons and her portrayal became a cultural reference and camp archetype for the spoiled "bad girl" throughout the 1970s.^{[citation needed][7]}

Years later, in one of her stand-up routines, Arngrim described playing Nellie on Little House on The Prairieas "like having PMS for seven years."^[8] In 2002, she was honored by the Young Artist Foundation with its Former Child Star "Lifetime Achievement" Award for her work as a child actress on Little House.^[9] At the 2006 TV Land Awards, Arngrim tied with Danielle Spencer ('Dee' on What's Happening!!) as the "Character Most in Need of a Time-out" for her role as Nellie.