| Birthname: | Thomas J. O'Brien |
| Minister From3: | United States |
| Country3: | Denmark |
| Term Start3: | May 27, 1905 |
| Term End3: | June 5, 1907 |
| President3: | Theodore Roosevelt |
| Predecessor3: | Laurits S. Swenson |
| Successor3: | Maurice Francis Egan |
| Ambassador From2: | United States |
| Country2: | Japan |
| Term Start2: | October 15, 1907 |
| Term End2: | August 31, 1911 |
| President2: | Theodore Roosevelt William Howard Taft |
| Predecessor2: | Luke E. Wright |
| Successor2: | Charles Page Bryan |
| Ambassador From1: | United States |
| Country1: | Italy |
| Term Start1: | November 13, 1911 |
| Term End1: | September 17, 1913 |
| President1: | William Howard Taft |
| Predecessor1: | John G. A. Leishman |
| Successor1: | Thomas Nelson Page |
| Birth Date: | 1842 7, df=yes |
| Party: | Republican |
| Spouse: | Delia Howard O'Brien (1848 - 1926) |
| Children: | 2 |
| Alma Mater: | University of Michigan |
| Profession: | Politician, diplomat |
| Signature: | Signature of Michigan politician Thomas James O’Brien.png |
Thomas James O’Brien (July 30, 1842 – May 19, 1933) was a politician and diplomat from the U.S. state of Michigan.
O'Brien was born in Jackson, Michigan, on July 30, 1842, the son of Timothy O'Brien and Elizabeth Lander O'Brien. On September 4, 1873, he married Delia Howard (July 14, 1848 - January 22, 1926).
O'Brien was a lawyer by profession and a Republican politician. In 1883 he was an unsuccessful candidate for the office of Justice of the Michigan Supreme Court. In 1896 and 1904 he was a delegate to the Republican National Convention from Michigan.
O’Brien, a graduate of the University of Michigan law school, held the following posts as ambassador of the United States:
O’Brien died on May 19, 1933.[1] He is buried with his wife at Oakhill Cemetery in Grand Rapids, Michigan.