William Smith O'Brien (1803 – 1864) is usually remembered as leader of the 'Rebellion' at Ballingarry, County Tipperary, in July 1848. For his part in it he was convicted of high treason and transported to Van Diemen's Land (Tasmania) where he spent five years.

It is said that he was a descendant of Brian Boru. O'Brien spent seventeen years of his life fighting for Irish interests in the British House of Commons. He was a representative figure of public opinion in Ireland in the first half of the nineteenth century, although overshadowed by Daniel O'Connell.

After O'Connell, he was the most celebrated figure in Irish public life at the time. But he was aloof in manner and spoke with an English accent so never enjoyed the adulation of the people as did the older man.

There is a monument dedicated to him on O'Connell Street, Dublin.