McCauley, Leo Thomas (1895–1974), diplomat, was born 29 December 1895 in Derry city, the third son of William McCauley of Woolwich, London, and Agnes McCauley (née Heaney). He was educated at St Columb's College, Derry, and UCD, where he later lectured in Latin and Greek (1916–21). McCauley was called to the bar in 1921 and practised in Dublin until 1923, when he entered the Department of Finance. He served as private secretary to the minister for finance, and was secretary to the budget committee, secretary to the committee on coinage design, and secretary to the tariff commission.
In 1929 he transferred to the Department of External Affairs. His first appointment was as first secretary (later chargé d'affaires) at the Irish legation in Berlin (1929–33). He was the only Irish diplomat in Berlin to witness the taking of power by the Nazi party and was an astute observer of Hitler's first months in office, recording his views in his confidential reports to his superiors in Dublin. One month after Hitler's accession McCauley wrote to Dublin that Hitler was ‘a mystical and mysterious figure: no one knows what his principles and true policy really are, and one can only speculate as to his statesmanship’ (McCauley to Walshe, 28 Feb. 1933, Documents, iv, 223). In early autumn of 1933 McCauley transferred to the Holy See as chargé d'affaires. He had expected to stay in Europe for some years, but was posted as consul general to New York in 1934, a post he held until 1946. In 1939 and 1940 he was commissioner general for Ireland to the New York World's Fair. In 1946 he returned to Dublin as assistant secretary at External Affairs and was minister plenipotentiary at Madrid (1949–50). Three ambassadorial appointments followed: Madrid (1950–55), Ottawa (1955–6), and the Holy See (1956–62).
McCauley retired from External Affairs in 1962. He lectured in history at Georgetown University, Washington, DC (1963–4), and acted as a community service consultant for the City Bank and Trust Co. (1965–8). He was awarded the Knight Grand Cross of the Order of Queen Isabel of Spain and the Knight Grand Cross of the Order of Pope Pius IX. He died 24 July 1974.
He married Georgia, daughter of Thomas O'Gorman of Elmhurst, New York; they had no children.