Dublin South by-election, 1925

This is a list of all by-elections (Irish: fothoghcháin) to Dáil Éireann, the lower house of the Irish parliament (Oireachtas) since 1923. By-elections in Ireland occur to fill vacant seats which can be caused by the death, resignation or expulsion of a sitting Teachta Dála (Member of Parliament).

There have been 130 by-elections since 1923, to fill 132 vacancies. 92 of these were caused by the death of a sitting Teachta Dála (TD). There have been six by-elections during the lifetime of the 31st Dáil. There were no by-elections during the 1st,2nd,3rd, 7th, 9th, 11th, 22nd, 25th and 26th Dála. The longest period without a by-election was almost 10 years between 1984 and 1994. The largest number of by-elections on one day was on 11 March 1925, when seven constituencies filled nine vacancies caused by the National Party's split from Cumann na nGaedheal. Those seven by-elections included two which filled two vacancies, via the single transferable vote. All the other by-elections have used its single-winner analogue, the alternative vote.

There have been 22 TDs who were first elected at a by-election and never subsequently re-elected at a general election. The only person twice elected at by-elections was Thomas Hennessy.

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