Pirrie served as the mayoress of Belfast in 1896 and 1897 when her husband served as lord mayor, described by
Frederick Hamilton-Temple-Blackwood, 1st Marquess of Dufferin and Ava as "the most charming and most popular lady mayoress who ever sceptred a city or disciplined a husband". The Pirries' greatest contribution to Belfast city was their fund-raising work for the new
Royal Victoria Hospital, which was to replace the old Belfast General Hospital and to celebrate
Queen Victoria's diamond jubilee. Under Pirrie's direction the campaign to raise £100,000 to build a 300-bed hospital was reached in under a year. Her husband donated £5,000, and she gave £2,000, and later gave an additional £11,000 to ensure the project was completed debt free. She later campaigned to raise a further £100,000 endowment for the hospital for expansion and running costs. This allowed for the purchase of equipment, resulting in two of the wards being named after the Pirries. She raised an additional £10,000 to name a ward in honour of her doctor, Professor
James Cuming. She served as chair on the ladies' committee and the nursing committee. She was recognised as the single most important benefactor of the hospital, serving as the president of the hospital from 1904 until her death. In 1929 and 1931, she donated 1,000 guineas and £1,000 to buy radium for cancer treatment, and would give generous Christmas gifts to patients and staff every year. She would extend these gifts to shipyard employees. Pirrie took an intense dislike to the new managing director, and attempted to undermine his position, even going so far as to appear to challenge his leadership on a number of occasions including a meeting of the works committee she chaired in late 1924 in Belfast. She later accepted the new arrangements, and sold her homes in England, with her Belfast home being taken over by the new managing director. ==Death and legacy==