Thomas O’Brien, Tom O’Brien, or Tommy O'Brien may refer to:
Politicians Thomas C. O'Brien (1887–1951), American politician and lawyer Thomas J. O'Brien (Illinois politician) (1878–1964), Illinois politician Thomas J. O'Brien (Massachusetts politician) (contemporary), Massachusetts state representative Thomas J. O'Brien (Michigan politician) (1842–1933), Michigan politician and U.S. ambassador Thomas P. O'Brien (born 1960), former United States attorney for the Central District of California Sir Tom O'Brien (trade unionist) (1900–1970), British trade unionist and member of parliament
Sportspeople Thomas O'Brien (footballer) (born 1991), Scottish footballer Tom O'Brien (American football) (born 1948), former American college football coach at NC State Tom O'Brien (footballer, born 1889) (1889–1963), Australian rules footballer for University Tom O'Brien (footballer, born 1904) (1904–1983), Australian rules footballer for Melbourne Tom O'Brien (jockey) (born 1986), Irish jockey Tom O'Brien (outfielder) (1873–1901), Major League Baseball outfielder/infielder Tom O'Brien (second baseman) (1860–1921), baseball player Tommy O'Brien (baseball) (1918–1978), Major League Baseball outfielder Tommy O'Brien (rugby union), Irish rugby union player Tommy O'Brien (basketball), American basketball player
Others Thomas O'Brien (bishop) (1792–1874), Church of Ireland bishop of Ossory, Ferns, and Leighlin Thomas O'Brien (interior designer) (born 1961), American designer Thomas D. O'Brien (1859–1935), co-founder of William Mitchell College of Law Thomas J. O'Brien (bishop) (1935-2018), bishop of Phoenix, 1982–2003 Thomas W. O'Brien (1859–1916), Canadian entrepreneur and pioneer Thomas Alexander O'Brien (1888–1948), New Zealand cinema owner and entrepreneur Thomas Enraght O'Brien (1827–1896), lord lieutenant of Limerick Tom O'Brien (actor, born 1890) (1890-1947), American film actor Tom O'Brien (actor) (born 1965), American film actor Tom O'Brien (swindler) (1851–1904), American confidence man and swindler Tommy O'Brien (actor, born 1983) American film actor and director