In the 1918 general elections the newly reformed Sinn Féin party had secured a large majority of Irish seats in the Parliament of the United Kingdom.

[1] This electoral success provided a propaganda coup for Sinn Féin, and so the British Government introduced the Local Government (Ireland) Act 1919, which allowed for parliamentary elections by proportional representation in all of Ireland for the first time, by the system of the single transferable vote for multi-member electoral areas.

The government hoped that the new system would reveal less-than-monolithic support for Sinn Féin, and it was first tested in the 1920 local elections.

[2][3] Some Sinn Féin members including Arthur Griffith had also helped to form the Proportional Representation Society of Ireland in the different circumstances of 1911.

Since 5 councillors was a quorum, Mayo County Council mandated a special election for 15 March, but only one extra candidate was nominated.