Justice Fitzgerald graduated with an LLB (Senior Scholar) from Victoria University of Wellington in 1992 and was admitted to the New Zealand bar in the same year.

Justice Fitzgerald joined the Wellington office of Russell McVeagh as a solicitor in 1992, before relocating to London in 1994, where she was admitted as a Solicitor of the Supreme Court of England and Wales in 1999.  She worked as a Senior Solicitor at Clifford Chance until 1997, and then at Debevoise & Plimpton from 1998 to 2001.

In 2001 Justice Fitzgerald returned to Russell McVeagh in Wellington. In 2003 she became a Senior Associate, Dispute Resolution at Sydney firm, Mallesons Stephen Jaques, and was admitted as a solicitor of the Supreme Court of New South Wales in 2003.

She returned to Auckland in 2006, and joined the partnership of Russell McVeagh in 2007, specialising in complex commercial dispute resolution, including regulatory investigations and proceedings, tax litigation, and arbitration law and practice.

Justice Fitzgerald was appointed a Judge of the High Court in 2016.  From February 2020 to August 2023, she was the Auckland Criminal List Judge, with oversight of all criminal jury trials in the Auckland High Court.  She was appointed the Chief Judge of the High Court of New Zealand in December 2023.