Dillon (1814-66) was a co-founder of the Nation newspaper and a leading member of the Young Ireland group. After the attempted rising in 1848 he escaped to the United States, where he worked as a lawyer for eight years. He was a critical observer of the contemporary scene - post-Famine Ireland, Irish-America and the Church of Pio Nono. His weekly letters to his wife, besides their intrinsic human interest, proved to be a particularly valuable source of research material. After returning to Dublin, Dillon, despite his rebel past and liberal Catholicism, co-operated with Archbishop Paul Cullen in forming the National Association. Elected MP for Tipperary in 1865, Dillon made a remarkable impression during his brief parliamentary career. His performance influenced Gladstone’s reshaping of Irish policy and left its mark on that statesman’s reforming ministry of 1868-74. His strategy of supporting the new liberal leadership was dramatically successful. He outlined ideas which would be implemented under Parnell ably assisted by his son, John Dillon. This contextual biography of Dillon is long overdue, it is based on primary sources, mainly the Dillon papers in Trinity College, Dublin.