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.