The 1920 Ballaarat by-election was held on 10 July 1920 to elect the member for Ballaarat in the Australian House of Representatives.
At the 1919 federal election, Nationalist candidate Edwin Kerby defeated the sitting Labor MP Charles McGrath by a single vote, the narrowest margin in Australian electoral history. McGrath challenged the result successfully on the grounds of electoral irregularities, triggering the by-election, at which McGrath was victorious.