The 1840 Connecticut gubernatorial election was held on April 1, 1840. It was a rematch of the 1839 Connecticut gubernatorial election. Incumbent governor and Whig nominee William W. Ellsworth was re-elected, defeating former senator and Democratic nominee John M. Niles with 54.17% of the vote.
After his loss, Niles would be appointed Postmaster General by PresidentMartin Van Buren, serving from May 19, 1840, until the end of Van Buren's term, March 4, 1841.