William Smith O'Brien (17 October 1803 – 18 June 1864) is an Irish Nationalist and Member of Parliament (MP) and leader of the Young Ireland movement.

He is convicted of sedition for his part in the Young Irelander Rebellion of 1848, but his sentence of death is commuted to deportation to Van Diemen's Land.

In 1854, he is released on the condition of exile from Ireland, and he lives in Brussels for two years.

In 1856, O'Brien is pardoned and returns to Ireland, but he is never active again in politics.