Monaghan was a parliamentary constituency represented in Dáil Éireann, the lower house of the Irish parliament or Oireachtas from 1921 to 1977.
The constituency elected 3 deputies (Teachtaí Dála, commonly known as TDs) to the Dáil, on the system of proportional representation by means of the single transferable vote (PR-STV).
It was abolished under the Electoral (Amendment) Act 1974, when it was replaced by the new constituency of Cavan–Monaghan which was first used at the 1977 general election.
Following the election of Fianna Fáil TD Erskine H. Childers as President of Ireland, a by-election was held on 27 November 1973.
The seat was won by the Fine Gael candidate Brendan Toal.