John Joseph Brennan (1913 – 1976) was a Northern Irish politician. He stood for the British House of Commons in Belfast West at the 1959 United Kingdom general election, representing the Independent Labour Group, receiving 37.6% of the vote.
In 1962, he stood for the Belfast Falls constituency at the 1962 Northern Ireland election, before becoming a founder member of the National Democratic Party.
Under the National Democratic banner, Brennan won Belfast Central at the 1965 Northern Ireland election without facing an opponent – the only member of that party to win election at this level.
However, at the 1969 Northern Ireland election, he was defeated by Paddy Kennedy of the Republican Labour Party.