The twelfth Minnesota Legislature first convened on January 4, 1870. The 11 members of the Minnesota Senate who represented even-numbered districts were chosen in the General Election of November 3, 1868, while the 11 members of the Minnesota Senate who represented odd-numbered districts, and the 47 members of the Minnesota House of Representatives, were chosen in the General Election of November 2, 1869.
The legislature met in a regular session from January 4, 1870 to March 4, 1870. There were no special sessions of the 12th Minnesota Legislature.