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 (1879) and Boston Red Caps (1880) of the National League. A native of Boston, Massachusetts, Sullivan attended Boston College and College of the Holy Cross. Listed at 5 ft 9 in (1.75 m), 170 lb., he threw right-handed (unknown batting side). Sullivan died at the age of 67 in his homeland of Boston, Massachusetts.