Denis James O'Sullivan (5 March 1918 – 20 July 1987) was an Irish Fine Gael politician. He was first elected to Dáil Éireann at his second attempt at the 1951 general election. He served as a Fine Gael Teachta Dála (TD) for various Cork constituencies until losing his seat at the 1965 general election. He served in the Second Inter-Party Government of John A. Costello as Government Chief Whip. He was a member of Seanad Éireann from 1965 to 1969.