| Nationality: | Irish |
| Office: | Senator |
| Term Start: | 23 June 1965 |
| Term End: | 5 November 1969 |
| Constituency: | Industrial and Commercial Panel |
| Office1: | Parliamentary Secretary |
| Suboffice1: | Government Chief Whip |
| Subterm1: | 1954–1957 |
| Suboffice2: | Defence |
| Subterm2: | 1954–1957 |
| Office3: | Teachta Dála |
| Term Start3: | October 1961 |
| Term End3: | April 1965 |
| Constituency3: | Cork Mid |
| Term Start4: | May 1951 |
| Term End4: | October 1961 |
| Constituency4: | Cork North |
| Birth Date: | 5 March 1918 |
| Birth Place: | County Cork, Ireland |
| Death Place: | County Cork, Ireland |
| Party: | Fine Gael |
Denis James O'Sullivan (5 March 1918 – 20 July 1987) was an Irish Fine Gael politician.[1] He was first elected to Dáil Éireann at his second attempt at the 1951 general election.[2] 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.[1]