[2] Diamond was an active nationalist before the Second World War and in 1933 was sentenced to a month in jail for refusing to pay a fine given out for addressing an illegal rally in support of republican prisoners.
He stood for the Westminster constituency of Belfast West in the October 1964 general election, but was defeated by James Kilfedder.
The campaign was disfigured by riots after Ian Paisley attempted to lead a Unionist crowd up Divis Street to remove an Irish tricolour from the offices of Sinn Féin, who were supporting the candidacy of Billy McMillen.
[4] Diamond saw a strong challenge to his position from the resurgent Northern Ireland Labour Party (NILP) in the late 1960s, and was criticised for being inattentive to his constituents' needs.
Paddy Devlin of the NILP, a former supporter of the reformists in the Belfast branch of the Irish Labour Party, defeated him in the 1969 Northern Ireland general election.