John Thomas O'Brien
- Bats Right, Throws Right
- Height 5' 9", Weight 170 lb.
- School Seattle University
- High School St. Mary's High School (South Amboy)
- Debut April 19, 1953
- Final Game July 19, 1959
- Born December 11, 1930 in South Amboy, NJ USA
Johnny O'Brien broke into the major leagues as an infielder, then converted into mainly a pitcher, and ended up his major league career as an infielder again. Oddly enough, his best year as a hitter was in the year that he was mainly a pitcher.
Johnny was the double play partner and twin brother of Eddie O'Brien. They spent most of their careers as teammates and basketball stars at Seattle University, and then with the Pittsburgh Pirates, and they both missed the 1954 season due to military service. During the three seasons that Johnny pitched at the major league level, Eddie also pitched some, albeit in only five games.
As a major league rookie, Johnny O'Brien became the regular second baseman for the Pirates in 1953, at team which lost 104 games. After spending a year in the military, in 1955 with the Pirates he hit .299 with above-average range in the infield. In 1956 he hit only .173 in 73 games but began his major league pitching career with a 2.84 ERA in eight games. The following year, 1957, he was in 16 games as a pitcher but was ineffective, while he hit .314. Thereafter, he pitched in only one more game and was primarily in the infield once again.
O'Brien was elected King County commissioner and councilman in Washington State from 1962 to 1973. He is the grandfather of Riley O'Brien.