Cavan was a parliamentary constituency represented in Dáil Éireann, the lower house of the Irish parliament or Oireachtas from 1921 to 1977.
The method of election was proportional representation by means of the single transferable vote (PR-STV).
From 1921 to 1923, Cavan elected 3 deputies (Teachtaí Dála, commonly known as TDs).
Following the resignation of Cumann na nGaedheal TD Seán Milroy, a by-election was held on 11 March 1925.
The seat was won by the Cumann na nGaedheal candidate John Joe O'Reilly.