Thomas or Tom O'Neill may refer to:

• Thomas O'Neill (Wisconsin politician) (1821–?), member of the Wisconsin State Assembly from Milwaukee Co
• Thomas J O'Neill (1849–1919), American merchant
• Thomas O'Neill (Canadian politician) (1882–1965), Canadian politician, member of Parliamentunty
• Thomas F. O'Neill (1890–1974), American art director
• Thomas O'Neill (journalist) (1904–1971), American writer for the Baltimore Sun
• Tip O'Neill (Thomas Phillip O'Neill Jr., 1912–1994), American politician
• Thomas P. O'Neill (historian) (1921–1996), Irish historian
• Tom O'Neill (ice hockey) (1923–1973), Canadian ice hockey player
• Thomas Newman O'Neill Jr. (1928–2018), United States federal judge
• Thomas P. O'Neill III (born 1945), American politician and leader of a public relations and government affairs firm
• Tommy O'Neill (born 1955), Scottish footballer

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