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 CIÉ, the state-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 at the 1981 general election and at both the February 1982 and November 1982 general elections. He did not contest the 1987 general election, and retired from politics.