Leask (Longfield), Ada Kathleen (1899–1987), historian and antiquary, was born 27 October 1899 in India, the eldest daughter of Major Alfred Percival Longfield (1862–1916) and Constance Ada Longfield (née Sanders) (d. 1967) of Edinburgh. Owing to her poor health she spent much of her youth with relatives in west Cork. She had a distinguished career at TCD, winning prizes each year and graduating BA and LLB in 1921. She went on to study at the London School of Economics, graduating MA in 1926. Her thesis on Anglo-Irish trade in the sixteenth century was published in 1929. She worked briefly as a teacher before taking up a position with the art and industrial section of the National Museum of Ireland in 1932; she was among the last employees of the museum to receive training from the Victoria and Albert Museum in London.
Her career with the National Museum came to an end in 1939 when in January 1940 she married the architect and archaeologist Harold G. Leask (qv). However, she continued to pursue her own research, and in the period that followed produced books and articles on textiles, wallpaper, wall-paintings, tombstones, embossed pictures, and Irish delftware. Her work for the Irish Manuscripts Commission resulted in the publication of The Shapland Carew papers (1946) and Fitzwilliam accounts 1560–65 (1960). She also assisted her husband in his archaeological inspections. Elected MRIA in 1952, she was an active member of the Royal Society of Antiquaries, the Irish Georgian Society, and the County Kildare Archaeological Society.
Ada Leask was a close friend of the poet John Betjeman, from his days as a Dublin resident. A keen supporter of the Irish language, she attended services in Irish at Christ Church Cathedral for many years. Widowed in 1964, she continued to research and publish despite the deterioration of her eyesight in the 1970s. She died 12 August 1987 in Dublin and was buried in Mount Jerome cemetery.