He trained as a teacher at Stranmillis University College, and there met active communist Edwina Menzies, the two marrying in 1954.

[3] He rapidly became a key figure in the party, editing Unity, its newspaper, completing the drafting of the party's programme, Ireland's Path to Socialism,[2] and becoming its Deputy General Secretary in 1964.

[3] In this role, he was active in the Northern Ireland Civil Rights Association, Belfast Trades Council.

He stood in the 1973 Northern Ireland Assembly election in Belfast West, but took last place with only 123 votes,[4] and came bottom of the poll for Belfast City Council at the 1977, 1981 and 1985 local elections.

[5][6] Stewart rose to become general secretary of the party in 1984, serving until 2001, when he instead became its chairman.