William Smith O'Brien (Irish: Liam Mac Gabhann Ó Briain; 17 October 1803 – 18 June 1864) was an Irish Nationalist and Member of Parliament (MP) and leader of the Young Ireland movement. He was convicted of sedition for his part in the Young Irelander Rebellion of 1848, but his sentence of death was commuted to deportation to Van Diemen's Land. In 1854, he was released on the condition of exile from Ireland, and he lived in Brussels for two years. In 1856 O'Brien was pardoned and returned to Ireland, but he was never active again in politics.