Peter James O'Brien (8 June 1874 – 28 September 1947) was a New Zealand politician of the Labour Party.

His parents of Irish descent were Terence O’Brien, a miner, and Bridget O’Leary.

After having worked as a miner in various Australian states, O'Brien emigrated to New Zealand in 1904 and found employment as a coalminer in Reefton.

[3] He lost the electorate in the 1925 election to Tom Seddon, but won it back in 1928, and held it to 1947, when he died.

[5] He remained an MP until his death, which caused a by-election held in December 1947 that was won by Labour's Jim Kent.