Senator O'Brien may refer to:
Anna Belle Clement O'Brien (1923–2009), Tennessee State Senate Charles H. O'Brien (1920–2007), Tennessee State Senate Duncan T. O'Brien (1895–1938), New York State Senate Henry L. O'Brien (1869–1935), New York State Senate James H. O'Brien (1860–1924), New York State Senate James O'Brien (U.S. Congressman) (1841–1907), New York State Senate Jay O'Brien (Virginia politician) (born 1951), Virginia State Senate Jeremiah O'Brien (Maine politician) (1778–1858), Maine State Senate Leo P. O'Brien (1893–1968), Wisconsin State Senate Margaret O'Brien (politician) (born 1973), Michigan State Senate Sean O'Brien (Ohio politician) (born 1969), Ohio State Senate Shannon O'Brien (Massachusetts politician) (born 1959), Massachusetts State Senate Ted O'Brien (born 1956), New York State Senate
See also James O'Bryan Jr. (born 1956), U.S. Virgin Islands State Senate Senator Bryan (disambiguation)