Mary O'Brien Harris (1865 – 19 April 1938) was a British politician.
Born Mary O'Brien, she was educated at Somerville College, Oxford.[1] She joined the Fabian Society in 1894, and served on its executive committee from 1898 until 1901. She remained involved with the organisation, and was a prominent figure in the Fabian Women's Group for many years.[2] She was also a founder member of the Socialist Quaker Society.[1]
O'Brien married J. Theodore Harris, and added his surname to her name. She served as headteacher of Clapton Girls' Academy for many years.[1]
In 1934, O'Brien Harris was elected to the London County Council as a Labour Party member, representing Hackney Central, and she held the seat until her death, in 1938.[2]