William Smith O'Brien (; 17 October 1803 – 18 June 1864) was an Irish politician. At one point he was a member of the British Parliament. Later on he was a nationalist and leader of the Young Ireland movement and led a rebellion against British rule in the 1840s during the Potato Famine. He was convicted of treason, a felony, and could have been executed, but he was exiled to Van Diemen's Land instead. In 1856, he was pardoned and allowed to return.