William O'Brien (2 October 1852 - 25 February 1928) was an Irish nationalist, journalist, agrarian agitator, social revolutionary, politician, party leader, newspaper publisher, author and Member of Parliament (MP.) in the House of Commons of the United Kingdom of Great Britain and Ireland . He was particularly associated with the campaigns for land reform in Ireland during the late 19th and early 20th centuries as well as his conciliatory approach to attaining Irish Home Rule.

William O'Brien was the seventh head football coach for the Southern Illinois Salukis in Carbondale, Illinois and he held that position for three seasons, from 1952 until 1954. His overall coaching record at SIU was 6 wins, 20 losses, and 0 ties. This ranks him 12th at SIU in terms of total wins and 16th at SIU in terms of winning percentage.

William O'Brien (6 March 1918 - 5 November 1994) was a Fine Gael politician from County Limerick in Ireland. He was a senator from 1969 to 1977, and then a Teachta Dála (TD) for Limerick West from 1977 to 1987.

Before entering politics, O'Brien was an employee of Córas Iompair Éireann (CIÉ), the sate-run Irish transport company.

He stood unsuccessfully as a Fine Gael candidate for Dáil Éireann in the Limerick West constituency at the 1969 and 1973 general elections before winning the seat at the 1977 general election. After his 1969 defeat, he was elected to the 12th Seanad Éireann on the Labour Panel, which returned him in 1973 to the 13th Seanad.

Once in the Dáil, O'Brien was re-elected in 1981 and at both the February 1982 and November 1982 elections. He did not contest the 1987 general election, and retired from politics.