The 1931 Upper Hunter state by-election was held on 13 June 1931 for the New South Wales Legislative Assembly electorate of Upper Hunter because of the death of William Cameron (). The Country Party did not nominate an official candidate because the seat had been held by the Nationalist Party. Malcolm Brown was nominated as an independent country candidate, and was supported in his campaign by the leader of the Country Party, Michael Bruxner.
<includeonly> William Cameron () died.</includeonly><noinclude> Malcom Brown won the seat on Labor preferences, and joined the Country Party once he entered Parliament.</noinclude>