Brosnan Walsh attended the Dominican Convent on Eccles Street before pursuing a career with market researcher ACNielsen.

[4] Brosnan Walsh played the character of Mags Kelly in Fair City for nearly twenty years before her January 2009 departure.

Her colleague Dave Duffy, who portrays Leo Dowling, said she got a "terrific send-off" with "champagne and flowers for her and a bit of a party in McCoy's Pub".

[4] After Brosnan Walsh's death on 20 December 2009 at age 71,[8] the cast of Fair City released the following tribute: "She was warm and lovely in person, a consummate professional and a delight to work with.

[2] Jane Gogan, RTÉ's drama recruiter, said "She has been at the heart of Fair City for the last 20 years and was without doubt one of its most popular characters.

[2][9][10] In 1969 she was a cast member of The Caucasian Chalk Circle Strand Players production and they won the Esso Trophy at the all-Ireland drama festival held in Athlone, County Westmeath.