Following her studies Gearin worked in Sydney. In 1986 the Northern Territory Attorney General's Department recruited Gearin, who was soon promoted to the role of senior litigation solicitor. She was called to the Bar by invitation in 1989. She was the first woman barrister in the Northern Territory and joined William Forster Chambers in January 1990.
During her career, Gearin was active in community and social organisations; she worked with other women to establish the first women's refuge in Darwin in 1988 and helped establish community legal services and refugee advocacy in Darwin in the 1990s.[2]
In 1992 she was awarded a Northern Territory Women's Fellowship by the Northern Territory Government and travelled to the USA with fellow lawyer Judy Harrison to research responses to domestic violence.[3] The resulting book and recommendations contributed significantly to policy developments in the field, both in the Northern Territory and nationally.[2]
In the early 2000s she was the President of the NT Chapter of the International Commission of Jurists and was an official observer at the War Crimes Tribunal hearings in Dili in 2002. She was a founder of the NT Women Lawyers Association in 1987 and the Australian Women Lawyers Association in 1997.
Gearin was recognised nationally as a Trailblazing Woman Lawyer in 2016, one of only 45 in the country. Her interviews are held in the National Archives.
Gearin retired from the Bar in 2010. Since then she has served on a number of Tribunals and was for 5 years the legal advisor to the Northern Territory Legislative Assembly on Human Rights and Rule of law compliance in NT legislation. She served as a part time member on NTCAT for 8 years and was in September 2025 appointed NT Legal Aid Commissioner representing community interests.
In 2025 Gearin was voted Northern Territory Professional Woman of Year.
In 2026 Gearin was appointed for 3 years as the NT Liquor Commissioner.
