John Lavin (1879 or 1880 – 6 August 1919) was an Irish trade unionist and socialist activist.
He traveled to San Francisco and settled in the city, joining both the Socialist Labor Party of America and the Industrial Workers of the World.
He became active in the Yorkshire Miners' Association (YMA) and also joined the British Socialist Labour Party (SLP) and the Workers' International Industrial Union.
There, he worked with Owen Ford to form a local branch of the SLP based in Mansfield, which attracted members including Rose Smith.
[2] Shortly afterwards, the entirety of the Mansfield SLP joined the Communist Party of Great Britain.