Mary O'Brien Harris (née O'Brien) (1865-19 April 1938) was a school teacher and local politician.
A member of the Society of Friends or "Quakers", she was one of the founders of the Socialist Quaker Society in 1898 along with Joseph Theodore Harris (1870-1958). The two married in 1901 and she adopted the surname "O'Brien Harris".
She joined the Labour Party, she stood unsuccessfully for election to the London County Council in 1931 at Hackney Central. At the 1934 council election she was elected and was re-elected in 1937, dying in the following year aged 72.
Principal of Clapton Girls' Grammar School.
One of the founder members of the National Association of Labour Teachers (NALT). (Politics & People of London: London County Council, 1889-1965 edited by Andrew Saint)
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