John Patrick Marcus "Jack" Kavanagh (12 July 1879 – 6 July 1964) moved to Australia in 1925, and was a central leader of the Communist Party of Australia until 1930, when the Stalinist Comintern removed him from the leadership. He was expelled from the party in January 1931, readmitted, and then expelled a second time in 1934 after being accused of Trotskyism. In 1940, Kavanagh joined the Communist League of Australia which was the Australian section of the Fourth International.
His wife's name was Kylsea, and he had one brother, Quinn.