John Ignatius Armstrong AC (10 July 1908 – 10 March 1977) was an Australian politician and diplomat. He served as a Senator for New South Wales from 1938 to 1962, representing the Labor Party, and was a minister in the Chifley Government. Armstrong later served as Lord Mayor of Sydney from 1965 to 1967, and then as High Commissioner to the United Kingdom from 1973 to 1974.