Missouri state elections in 2020 were held on Tuesday, November 3, 2020.

[1] To vote by mail, registered Missouri voters had to request a ballot by October 21, 2020.

Another seat is open after the incumbent, Lacy Clay, lost renomination in its Democratic primary.

[33] Missouri Amendment 3, Redistricting Process and Criteria, Lobbying, and Campaign Finance Amendment is to amend the state constitution to lower thresholds for lobbyists' gifts, lower campaign contribution limits for state senate campaigns and reverse changes to the redistricting process brought about by the passage of 2018's Missouri Amendment 1, known as "Clean Missouri".

That amendment (aimed to prevent gerrymandering[34]) delegated redistricting to a nonpartisan state demographer and citizens' commission as opposed to the status quo ante of it being left to a bipartisan commission appointed by the governor.