Everard McDonnell O'Brien (9 April 1907 – 17 August 1971) was an Australian politician who was a Labor Party member of the Legislative Assembly of Western Australia from 1952 to 1959, representing the seat of Murchison.
O'Brien was born in Nunngarra, a locality near the town of Sandstone in Western Australia's Mid West region.
O'Brien returned to the Mid West in the 1940s, prospecting at Big Bell for a period and later serving as secretary of the Yalgoo Road Board.
He first ran for parliament at a 1947 Legislative Council by-election for Central Province, but lost to the Liberal Party's Harold Daffen.
[1] O'Brien eventually entered parliament at the 1952 Murchison by-election, which was caused by the death of the sitting Labor member, William Marshall.