Born in Waterford, Meagher was educated at Clongowes Wood and later trained as a barrister. He quickly entered political life and was a founder-member of the Irish Confederation. A fervent nationalist, who believed in an armed uprising, Meagher was arrested after a failed rising in 1848 and sentenced to death. The sentence was commuted and he was sent to Van Dieman's land (Tasmania) to serve a life sentence. In 1852, he escaped his island prison and fled to America where he became a journalist and lecturer. During the American Civil War, he organised the Irish Brigade to fight for the North and became a brigadier-general.