Londonderry was a county constituency of the Parliament of Northern Ireland from 1921 to 1929.

It returned five MPs, using proportional representation by means of the single transferable vote.

The House of Commons (Method of Voting and Redistribution of Seats) Act (Northern Ireland) 1929 divided the constituency into five constituencies elected under first past the post: City of Londonderry, Foyle, Mid Londonderry, North Londonderry and South Londonderry.

[1] In May 1921, Dáil Éireann, the parliament of the self-declared Irish Republic run by Sinn Féin, passed a resolution declaring that elections to the House of Commons of Northern Ireland and the House of Commons of Southern Ireland would be used as the election for the Second Dáil.

[2] All those elected were on the roll of the Second Dáil, but Eoin MacNeill, who was also elected for the National University of Ireland, was the only MP elected for Londonderry to sit as a TD in Dáil Éireann.