James O'Connor Kessack (19 October 1879 – 13 November 1916) was a British trade unionist. Born in Aberdeen, Kessack grew up in Huntly and Inverurie, and worked from an early age to support his family, his father struggling to find work, and both of his parents dying while he was young. He moved to Glasgow to find employment shortly before his father's death, and his younger siblings then moved in with him.