The 1851 United States Senate election in Wisconsin was held in the 4th Wisconsin Legislature on Incumbent Democratic U.S. senator Henry Dodge was re-elected to a full six-year term.
In the 1851 legislative session, Democrats held large majorities in both chambers and neither of the other parties bothered to make a formal nomination. The only real contest was in the Democratic caucuses, where Dodge narrowly won renomination.
The Democrats met in caucus on January 19 to select a nominee. Three Democrats were absent from the caucus, but they were joined by Free Soiler George Gale, who afterward became a Democrat. In the initial informal poll, Dodge had the support of only 22 of 61 legislators. His nearest opponent was Moses Strong, with 17 votes. Strong had been speaker of the previous session of the Assembly, and was considered the candidate of the western region of the state; Strong had also been instrumental in the maneuvering to rescind the resolution that had called for the resignation of U.S. senator Isaac P. Walker, seen as an effort to court Walker's eastern constituency.
Over the course of the evening, Dodge's vote count gradually crept up, while Strong faded. Dodge won the nomination on the fourth ballot with just 31 of 61 votes. As it turned out, George Gale's vote in the caucus proved decisive.