Mackintosh married in April 1868, Gertrude Niles Cook (d. 1925), daughter of Timothy Cook, J.P., of Strathroy, Ontario, and his wife, Harriet Terry, the daughter of Dr William Terry, ex-M.P.P., Niagara, Ontario, and granddaughter of Parshall Terry, M.H.A., a United Empire Loyalist, and member of the 1st Parliament of Upper Canada. Mrs Mackintosh was born at Strathroy, Ontario, and educated at a convent at London, Ontario. While wife of the mayor of Ottawa, in 1879, she assisted at the opening of the first Dominion Exhibition. Later, she assisted at the opening of the great North-West Exhibition, held in Regina in 1895. She served as vice-president in the Territories for the National Council of Women.