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.

Listed at 5 ft 9 in (1.75 m), 170 lb., he threw right-handed (unknown batting side).

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.

This biographical article relating to an American baseball third baseman is a stub.