John Marcus O'Sullivan (18 February 1881 – 9 February 1948) was an Irish Fine Gael politician who served as Minister for Education from 1926 to 1932 and Parliamentary Secretary to the Minister for Finance from 1924 to 1926. He served as a Teachta Dála (TD) from 1923 to 1943. He was married to Agnes Crotty, and they had 4 children, two sons and two daughters. O'Sullivan died on 9 February 1948, at his home in Rathgar, Dublin.