FitzGerald was raised in Camden, Maine. Her father, Des FitzGerald, is the former CEO of the ContiSea unit of the multinational corporation ContiGroup and the founder of Ducktrap River Fish Farm Inc. Her mother, Pam Allen, is the author of Knitting for Dummies and the founder of the yarn company Quince & Co. FitzGerald first developed an interest in acting as a child and performed in many community theatre and school productions. She was a boarding student at Concord Academy in Massachusetts. She later graduated from NYU's Tisch School of the Arts, where she studied drama at the Stella Adler Studio of Acting. FitzGerald also spent time studying Shakespeare at the Royal Academy of Dramatic Art in London.