The Fourth Wisconsin Legislature convened from January 8, 1851, to March 17, 1851 in regular session. Senators representing odd-numbered districts were newly elected for this session and were serving the first year of a two-year term. Assembly members were elected to a one-year term. Assembly members and odd-numbered senators were elected in the general election of November 5, 1850. 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.