John Thomas O'Brien (born December 11, 1930) is a former backup second baseman and pitcher in Major League Baseball who played for the Pittsburgh Pirates (1953, 1955–58), St. Louis Cardinals (1958) and Milwaukee Braves (1959). O'Brien batted and threw right-handed. His twin brother, Eddie, was also a major league infielder. O'Brien attended Saint Mary's High School in South Amboy, now Cardinal McCarrick High School, where he has been inducted into the school's sports hall of fame.