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. He went to school in Mount Margaret, and afterward worked as a labourer and shearer. In the 1930s, he went to live in Perth, working initially as a labourer and later as a rail and tram conductor. 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. He was re-elected at the 1953 and 1956 state elections, but at the 1959 election was defeated by the Liberal candidate, Richard Burt.^[2] O'Brien remained in Perth after leaving parliament, dying there in August 1971, aged 64. He married twice, and had seven children in total, one of whom, Simon O'Brien, became a Liberal member of parliament.^[1]