Hemingway was born November 22, 1961 in Mill Valley, California, the third daughter of Byra Louise (née Whittlesey) Hemingway and Jack Hemingway, a writer.

Her paternal grandparents were Hadley Richards on and writer Ernest Hemingway. She was named after the Cuban port of Mariel—her father and grandfather visited the village regularly to go fishing.

Mariel Hemingway's Family Tree