They had five children: Mary Theresa (Molly), Harry Gerard, Bernard, Patrick, and Nora.
In his early political career, O'Neill served as Chairman of the Warrenpoint Urban District Council, as well as Justice of the Peace, for a number of years.
Partition, which had created a northern Catholic and nationalist majority in a primarily Protestant and Unionist state, was a key issue in this election.
To protest the fact that Northern Ireland was established to have a Unionist majority, the Nationalist party members, including O'Neill, abstained from taking their seats during the first parliament.
The material available includes incoming and outgoing correspondence with constituents, government officials, supporters, and other MPs.