Gilbert was born in Los Angeles, California to a Jewish family. She was adopted by a couple, actor Paul Gilbert (birthname of Paul MacMahon) and his wife Barbara. As a former child actor, the naturally red-headed Melissa is best known for her role of Laura Ingalls on the television series Little House on the Prairie (1974-1983), originating the role of Barbara Gordon in Batman: The Animated Series and for her two terms as president of the Screen Actors Guild.

Her younger brother Jonathan Gilbert was also adopted, and would later act in some television shows with Melissa. When Melissa was eight, her adoptive parents divorced, and when she was eleven, her adoptive father died. Her adoptive mother had married Harold Abeles and gave birth in 1975 to Sara Abeles, who became an actress and in 1984 changed her surname to Gilbert, becoming Sara Gilbert, a star on Roseanne.

Melissa Gilbert regularly keeps in contact with her friend Alison Arngrim, who played her nemesis "Nellie Oleson" on Little House.

Gilbert married Bo Brinkman in 1988 and the couple had a son, Dakota Paul, in 1989.

She then married Bruce Boxleitner in 1995, and played his character's wife on Babylon 5. In real life, the two had a son whom she named after Michael Landon, her mentor and friend on Little House.

She won the Screen Actors Guild presidency in 2001 after a competitive election contest in which she ultimately beat her opponent Valerie Harper after a revote 21,351 votes to 12,613 votes. In July 2005, she announced that she would not seek a third term as president. She was succeeded by Alan Rosenberg who formally assumed the office of Guild president on September 25.

For her contribution to the television industry, Melissa Gilbert has a star on the Hollywood Walk of Fame at 6429 Hollywood Blvd. In 1998, she was inducted into the Western Performers Hall of Fame at the National Cowboy & Western Heritage Museum in Oklahoma City, Oklahoma.