John Mary Lynch (15 August 1917 – 20 October 1999) was an Irish Fianna Fáil politician who served as Taoiseach from 1966 to 1973 and 1977 to 1979. He was Leader of Fianna Fáil from 1966 to 1979, Leader of the Opposition from 1973 to 1977, Minister for Finance from 1965 to 1966, Minister for Industry and Commerce from 1959 to 1965, Minister for Education 1957 to 1959, Minister for the Gaeltacht from March 1957 to June 1957, Parliamentary Secretary to the Minister for Lands and Parliamentary Secretary to the Government from 1951 to 1954. He served as a Teachta Dála (TD) from 1948 to 1981.
Lynch was the third leader of Fianna Fáil from 1966 until 1979, succeeding Seán Lemass. He was the last party leader to secure (in 1977) an overall majority in the Dáil for his party. Historian and journalist T. Ryle Dwyer called him "the most popular Irish politician since Daniel O'Connell".