Thomas O'Brien
Thomas O’Brien, Tom O’Brien, or Tommy O'Brien may refer to:
- Thomas D. O'Brien, co-founder of William Mitchell College of Law
- Thomas J. O'Brien (Illinois politician) (20th c.), 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 J. O'Brien (bishop) (born 1935) Bishop of Phoenix from 1982 to 2003
- Thomas P. O'Brien, former United States Attorney for the Central District of California
- Tom O'Brien (UK politician) (1900–1970), British trade unionist and Member of Parliament
- Tom O'Brien (second baseman) (1860–1921), 19th century baseball player
- Tom O'Brien (outfielder) (1873–1901), MLB outfielder/infielder
- Tom O'Brien (actor) (born 1965), American film actor
- Tom O'Brien (American football) (born 1948), American college football coach at NC State
- Tom O'Brien (Australian rules footballer), Australian rules footballer for University
- Tom O'Brien (jockey) Steeplchase rider who competed in four Grand Nationals up to 2010
- Tommy O'Brien (1918–1978), MLB outfielder