| Denny Sullivan | |
| Position: | Third baseman |
| Bats: | Unknown |
| Throws: | Right |
| Birth Date: | June 26, 1858 |
| Birth Place: | Boston, Massachusetts |
| Death Place: | Revere, Massachusetts |
| Debutleague: | MLB |
| Debutdate: | August 25 |
| Debutyear: | 1879 |
| Debutteam: | Providence Grays |
| Finalleague: | MLB |
| Finaldate: | September 25 |
| Finalyear: | 1880 |
| Finalteam: | Boston Red Caps |
| Statleague: | MLB |
| Stat1label: | Batting average |
| Stat1value: | .261 |
| Stat2label: | Home runs |
| Stat2value: | 0 |
| Stat3label: | Runs batted in |
| Stat3value: | 3 |
| Teams: |
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Dennis J. Sullivan (June 26, 1858 – December 31, 1925) was an American utility player in Major League Baseball, playing mainly as a third baseman for the Providence Grays and Boston Red Caps of the National League. A native of Boston, Massachusetts, Sullivan attended Boston College and College of the Holy Cross. Listed at, 170 lb., he threw right-handed (unknown batting side).
In a six-game career, Sullivan was a .261 hitter (6-for-23) with six runs, three RBI, and two doubles without home runs. He made six appearances as a third baseman (4), catcher (1) and left fielder (1), and was a member of the Providence 1879 National League champions.
Sullivan died at the age of 67 in his homeland of Boston, Massachusetts.