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.

He was relegated to an unwinnable fourth position on Labor's ticket for the 1961 election and left parliament in July 1962.

[5] He died of a myocardial infarction in Batemans Bay, aged 68, survived by his wife, a son and four daughters.