By-elections in Ireland occur to fill vacant seats which can be caused by the death, resignation, disqualification or expulsion of a sitting Teachta Dála (member of parliament).
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.
Convention in the Commons was that the writ for a by-election be moved by a party colleague of the vacating member, which was impossible for the abstentionist Sinn Féin.
[9] Asked in the Civil War about filling Third Dáil vacancies, W. T. Cosgrave as Chairman of the Provisional Government stated "the condition of the country scarcely warrants the holding of elections".
[10] In the first Dáil, four Sinn Féin TDs represented two constituencies: Éamon de Valera, Arthur Griffith, Eoin MacNeill and Liam Mellowes.