Mary O'Brien Harris (1865 – 19 April 1938) was a British politician.
Born Mary O'Brien, she was educated at Somerville College, Oxford.
She remained involved with the organisation, and was a prominent figure in the Fabian Women's Group for many years.
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.