The 1948 Armagh by-election was held on 5 March 1948, following the death of Ulster Unionist Party Member of Parliament William Allen.
The Ulster Unionists selected James Harden, a former major in the British Army who had acted as senior liaison officer to Montgomery from early 1944.
[1] The Northern Ireland Labour Party had achieved some strong results in recent years, but had never stood in Armagh, and decided not to put forward a candidate for the by-election.
Geoffrey Bing stated in Parliament that impersonation took place at one polling station on "a really large scale", and that two election agents who arrived to investigate were attacked by a mob of two hundred people.
Harden, in response, noted that O'Reilly had agreed with him that, despite some incidents at the close of polling, the election was fair, and that he had seconded his vote of thanks to the returning officer.