West Mayo was a parliamentary constituency in Ireland, which returned one Member of Parliament (MP) to the House of Commons of the Parliament of the United Kingdom, elected on a system of first-past-the-post, from 1885 to 1922.
Prior to the 1885 general election the area was part of the two-seat Mayo constituency.
From 1922, on the establishment of the Irish Free State, it was not represented in the UK Parliament.
The 65.1% drop in the Irish Parliamentary Party vote is the largest decrease in a party's vote between successive House of Commons elections in a single constituency.
Between elections, the First World War and Easter Rising had changed the political landscape, and the Representation of the People Act 1918 had greatly increased the electorate.