Thomas H. O'Brien (June 22, 1860 – April 21, 1921) was an infielder in Major League Baseball who played for five clubs in parts of six seasons between 1882 and 1890.

He reached the majors in 1882 with the Worcester Ruby Legs (NL), spending one year with them before moving to the Baltimore Orioles (AA), 1883), Boston Reds (UA, 1884), again with Baltimore (1885), and the New York Metropolitans (AA, 1887) and Rochester Broncos (AA, 1890).

His most productive season came in 1884 with Boston, when he appeared in 103 games while hitting .263 with four home runs, 118 hits, 31 doubles, eight triples and 80 runs scored –all career-numbers.

In 270 games, O'Brien was a .231 hitter (257-for-1111), including 74 extra-base hits and 61 RBI.

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