Darnell was born in Dallas, Texas, as one of four children (excluding her mother's two children from an earlier marriage) to postal clerk Calvin Roy Darnell (1888–1977) and the former Margaret "Pearl" Brown (1892–1966). She was the younger sister of Undeen (b. 1918) and the older sister of Monte Maloya (b. 1929) and Calvin Roy, Jr. (b. 1930). Her parents were not happily married, and she grew up as a shy and reserved girl in a house of domestic turmoil. Starting at an early age, her mother, Pearl, had big plans for Darnell in the entertainment industry. She believed that Linda was her only child with potential as an actress and ignored the rearing of her other children.