The Irish Anti-Partition League (APL) was a political organisation based in Northern Ireland which campaigned for a united Ireland from 1945 to 1958.
Prior to the establishment of the League, there had been no organisation of Irish nationalists since the Irish Union Association and Northern Council for Unity had become inactive in the late 1930s. This became a major complaint among supporters of the Nationalist Party, and at the Northern Ireland general election, 1945, some Nationalists candidates - including Eddie McAteer and Malachy Conlon pledged that if they were elected, they would organise a convention with the intention of uniting all Irish nationalists in one membership organisation.
McAteer and Conlon were both elected, and on 14 November 1945 they presided over a convention in Dungannon. The convention was attended by about 480 people, including all Nationalist Party Members of Parliament (MPs) and Senators. Other anti-partitionist MPs were invited, but Socialist Republican Party MP Harry Diamond refused to attend.
The convention elected a standing committee. Conlon became its first Secretary and James McSparran its first Chairman. It also collected more than £1000 to begin campaigning activities.
Divisions appeared in the new organisation almost immediately. The Derry Journal, generally sympathetic to the nationalist cause, attacked two prominent members: T. J. Campbell for resigning as an MP in order to take up a position as a judge, and Cahir Healy for pledging to support the Ulster Unionist Party leadership of the Parliament in their campaign to withhold some Imperial Contributions in order to improve housing. A few months later, Thomas Maguire accused McSparran of rejecting a position as a judge solely because it was insufficiently well paid.