distinguished British public servant who was executed for treason and became one of the principal Irish martyrs in the revolt against British rule in Ireland.

Casement was a British consul in Portuguese East Africa (Mozambique; 1895–98), Angola (1898–1900), Congo Free State (1901–04), and Brazil (1906–11). He gained international fame for revealing atrocious cruelty in the exploitation of native labour by white traders in the Congo and the Putumayo River region, Peru; his Congo report (published 1904) led to a major reorganization of Belgian rule in the Congo (1908), and his Putumayo report (1912) earned him a knighthood.

Ill health forced Casement to retire to Ireland in 1912. Although he came from an Ulster Protestant family, he had always sympathized with the predominantly Roman Catholic Irish nationalists. Late in 1913 he helped form the Irish National Volunteers, and in July 1914 he traveled to New York City to seek American aid for that anti-British force. After World War I broke out in August, Casement hoped that Germany might assist the Irish independence movement as a blow against Great Britain. On arriving in Berlin in November 1914, he found that the German government was unwilling to risk an expedition to Ireland and that most Irish prisoners of war would refuse to join a brigade that he intended to recruit for service against England.

Later, Casement failed to obtain the loan of German army officers to lead the Irish rising planned for Easter 1916. In a vain effort to prevent the revolt, he sailed for Ireland on April 12 in a German submarine. Put ashore near Tralee, County Kerry, he was arrested on April 24 and taken to London, where, on June 29, he was convicted of treason and sentenced to death. An appeal was dismissed, and he was hanged at Pentonville Prison despite attempts by influential Englishmen to secure a reprieve in view of his past services to the British government. During this time, diaries reputedly written by Casement and containing detailed descriptions of homosexual practices were circulated privately among British officials. After years of dispute over their authenticity, the diaries were made available to scholars by the British home secretary in July 1959. It was generally considered that the passages in question were in Casement's handwriting.

In 1965 Casement's remains were returned to Ireland and, after a state funeral, reinterred in Dublin.