Roman Catholic prelate who became one of Australia's most controversial political figures during the first half of the 20th century.

Mannix studied at St. Patrick's College, Maynooth, County Kildare, where he was ordained priest in 1890 and where he taught philosophy (1891) and theology (1894); from 1903 to 1912 he served as president of the college. Consecrated titular archbishop of Pharsalus in 1912, he arrived in Melbourne in the following year as coadjutor archbishop, becoming archbishop of Melbourne in 1917.

Mannix's forthright demands for state aid for the education of Roman Catholics in return for their taxes and his opposition to drafting soldiers for World War I made him the subject of controversy. A zealous supporter of Irish independence, he made an official journey to Rome in 1920 via the United States, where his lengthy speechmaking attracted enthusiastic crowds. His campaign in behalf of the Irish, however, caused the British government to prevent him from landing in Ireland, which he finally visited in 1925.

After World War II Mannix sought to stop Communist infiltration of the Australian trade unions; he played a controversial part in the dissensions within the Australian Labor Party and backed the largely right-wing Catholic Democratic Labor Party, which broke away. A promoter of Catholic Action (i.e., lay apostolic activity in the temporal society) and of the Catholic social movement, he is responsible for having established 181 schools, including Newman College and St. Mary's College at the University of Melbourne, and 108 parishes.