| John Thomas Lenahan | |
| Image Upright: | .9 |
| State: | Pennsylvania |
| District: | 11th |
| Term Start: | March 4, 1907 |
| Term End: | March 3, 1909 |
| Preceded: | Henry Wilbur Palmer |
| Succeeded: | Henry Wilbur Palmer |
| Birth Date: | 15 November 1852 |
| Birth Place: | Jenkins Township, Pennsylvania |
| Death Place: | Wilkes-Barre, Pennsylvania |
| Party: | Democratic |
John Thomas Lenahan (November 15, 1852 – April 28, 1920) was a Democratic member of the U.S. House of Representatives from Pennsylvania.
John T. Lenahan was born in Jenkins Township, Pennsylvania. He graduated from Villanova College in 1870. He studied law at the University of Pennsylvania in Philadelphia, Pennsylvania. He was admitted to the bar in 1873 and commenced practice in Wilkes-Barre, Pennsylvania. He was a delegate to the Democratic National Conventions in 1892 and 1896.
Lenahan was elected as a Democrat to the Sixtieth Congress. He was not a candidate for renomination in 1908. He resumed the practice of law, and died in Wilkes-Barre. Interment in St. Mary's Cemetery.