| Thomas Clarke Theaker | |
| State: | Ohio |
| District: | 17th |
| Term Start: | March 4, 1859 |
| Term End: | March 3, 1861 |
| Preceded: | William Lawrence |
| Succeeded: | James R. Morris |
| Office2: | Commissioner of United States Patent Office |
| Term Start2: | August 17, 1865 |
| Term End2: | January 20, 1868 |
| Preceded2: | David P. Holloway |
| Succeeded2: | Elisha Foote |
| Appointer2: | Andrew Johnson |
| Party: | Republican |
| Birth Date: | 4 February 1812 |
| Birth Place: | York, Pennsylvania, US |
| Death Place: | Oakland, Maryland, US |
| Restingplace: | Weeks Cemetery, Bridgeport, Ohio, US |
Thomas Clarke Theaker (February 4, 1812 – July 16, 1883) was an American politician who served one term as U.S. Congressman from 1859 to 1861. He also served as commissioner of the United States Patent Office from 1865 to 1868.
Theaker was a native of York, Pennsylvania, but moved to Bridgeport, Ohio, in 1830, where he became a wheelwright and machinist.
Elected as a Republican to represent the Seventeenth Congressional District of Ohio in the Thirty-Sixth Congress, he failed to win re-election in 1860, but was appointed to a seat on the U.S. Patent Office's Board of Appeals.
On August 15, 1865, he was appointed commissioner of the Patent Office, a post he held until his resignation in January 1868.