The Fourth Wisconsin Legislature convened in regular session from January 8, 1851, to March 17, 1851.

Senators representing odd-numbered districts were newly elected for this session and served the first year of a two-year term.

Assembly members were elected to a one-year term.

Senators representing even-numbered districts were serving the second year of their two-year term, having been elected in the general election held on November 6, 1849.

[1] The governor of Wisconsin during this entire term was Democrat Nelson Dewey, of Grant County, serving the second year of his second two-year term, having won re-election in the 1849 Wisconsin gubernatorial election.