Gregson Wagner was born in Los Angeles, California, and is the daughter of American actress Natalie Wood (1938–1981) and British producer Richard Gregson (1930-2019). Her godmother was actress Ruth Gordon. Her parents separated when she was ten months old, and later divorced. Her mother remarried actor Robert Wagner in 1972, and together they had a daughter, Courtney Wagner (born 1974). Her aunt is actress and producer Lana Wood.