| Election Name: | 1840 Missouri gubernatorial election |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1836 Missouri gubernatorial election |
| Previous Year: | 1836 |
| Next Election: | 1844 Missouri gubernatorial election |
| Next Year: | 1844 |
| Election Date: | August 3, 1840 |
| Nominee1: | Thomas Reynolds |
| Party1: | Democratic Party (United States) |
| Popular Vote1: | 29,625 |
| Percentage1: | 57.15% |
| Nominee2: | John Bullock Clark |
| Party2: | Whig Party (United States) |
| Popular Vote2: | 22,212 |
| Percentage2: | 42.85% |
| Governor | |
| Before Election: | Lilburn Boggs |
| Before Party: | Democratic Party (United States) |
| After Election: | Thomas Reynolds |
| After Party: | Democratic Party (United States) |
The 1840 Missouri gubernatorial election was held on August 3, 1840. In the election, Democrat Thomas Reynolds defeated Whig candidate John Bullock Clark.
Thomas Reynolds would not live for the full length of this term, committing suicide on February 9, 1844,[1] and being replaced by Lt. Governor Meredith Miles Marmaduke.