Hearn, Mary Ellice Thorn (1891–1969), gynaecologist and first female fellow of the RCPI, was born 25 February 1891 at 17 St Patrick's Place, Cork, the daughter of William Edward Ashley Cummins (1858–1923), professor of medicine at UCC, and Jane Constable Cummins (née Hall). She had three sisters and two brothers. Of her sisters, Geraldine Cummins (qv) was a playwright, Jane was a squadron officer in the WRAF during the second world war and also became a medical doctor, and Iris Cummins (qv) was an engineer. Both of her brothers also became doctors, and one, N. Marshall Cummins, was involved in setting up the first blood transfusion service in Cork. Mary Cummins was a first-rate student at UCC, where she studied medicine, but she quit her course in the summer of 1911 to get married. However, her husband encouraged her to continue with her professional qualifications and she returned to UCC, graduating MB, B.Ch., BAO in 1919 with first-class honours and a distinction in medicine, her young son attending the conferring ceremony. She proceeded MD in 1922, when she was awarded first place and a special distinction in the examination. The following year she took membership of the RCPI, and in 1924 she became the first woman to achieve fellowship of the college.
Hearn was house surgeon and house physician at the North Charitable Infirmary in Cork before she was appointed to the Victoria Hospital Cork in 1922 as an honorary anaesthetist. In 1923 she joined the medical staff, first as assistant medical officer and then as medical officer, while also running a busy private gynaecological practice near Shandon in Cork. She gave lifelong service to the Victoria and was actively involved in the running of the hospital, serving on the board from 1938 onwards. Her talent at attracting donations to the hospital as well as the energy she put into organising fund-raising events, both for the hospital and for community causes, made her famous among her colleagues. The most popular of her annual fund-raisers was the tea and entertainment for outpatients at Christmas. In order to keep up with developments in her field, Hearn attended postgraduate courses in London every year until 1968. She also held appointments as the medical officer to the Rochelle School, Cork, and Midleton College, as well as that of honorary visiting physician to Lapps Charity in Cork.
Hearn had a deep religious faith and was universally remembered as a genuinely kind, generous, and caring person. Children were a constant source of happiness for her and she showed great kindness and thoughtfulness to new mothers whom she encountered through her work, especially those who were not well off. A keen sportswoman, she was a distinguished hockey player who represented Ireland (1908–12), and her family were much involved in the sport. She married Robert Thomas Hearn, the Church of Ireland bishop of Cork, Cloyne, and Ross, who died in 1952. They had two children. Their son, Robert, was a general practitioner in Rugby, England, and their daughter, Ellice, was a barrister in London who was made CBE for her work as a parliamentary draughtsman. Mary Hearn travelled to Buckingham Palace to watch her daughter receive her award. She lived at St Patrick's Hill in the centre of Cork and died 3 June 1969 after a brief illness, aged seventy-eight, at the Victoria Hospital. A memorial fund in her honour was set up by the hospital and the proceeds used to create a nurses' library.