Peter O'Brien, 1st Baron O'Brien

Peter O'Brien, Baron O'Brien (June 29, 1842 – 7 September 1914) was an Irish lawyer who became Lord Chief Justice of Ireland. Born the fifth son of John O'Brien, Liberal Member of Parliament for County Limerick, O'Brien was educated at Trinity College Dublin and was called to the bar in 1865. He joined the Munster circuit and built up a successful practice, and in 1880 became a Queen's Counsel. The following year he was appointed Junior Crown Counsel at Green Street, Dublin, becoming Senior in 1882, and was made a bencher of the King's Inns in 1884.

In 1887 O'Brien was appointed Ireland's Solicitor General, becoming Attorney General and an Irish Privy Counsellor the following year. He was finally appointed Lord Chief Justice in 1889, holding the office for twenty-four years. He was created a baronet in 1891, and in 1900 was ennobled as Baron O'Brien, of Kilfenora in the County of Clare. He died without male heirs at Airfield, Stillorgan, County Dublin, his barony and baronetcy thus becoming extinct.