[1] Initially, they were formed as local defensive organisations opposed to the Protestant Peep o' Day Boys; however, by 1790 they had become a secret oath-bound fraternal society made up of lodges.
[2] At Grangemore, near Ballymacnab, County Armagh, an area that had previously suffered from a Peep o' Day Boys raid, such a grouping was founded and became known as the Defenders.
[2] The Defenders started out as independent local groups, defensive in nature, however by 1790 they had merged into a widespread secret oath-bound fraternal organisation consisting of lodges, associated to a head-lodge led by a Grand Master and committee.
[2] Magistrates who were largely anti-Catholic and Protestant juries acquitted Peep o' Day Boys who were brought to trial whilst convicting and punishing Defenders.
[2] In 1788, Lord Charlemont's re-organised Volunteer companies in County Armagh became involved in the conflict as Peep o' Day Boys joined their ranks.
Although the terms of the Act stipulated that conscripts would serve in Ireland, it was widely believed that men would be sent abroad and the resultant opposition saw thousands taking the Defender oath.
[6] In September 1795 the Peep o' Day Boys, backed up by some Volunteer companies, and Defenders would clash in the short Battle of the Diamond, near Loughgall in County Armagh.
[7][10] The Society of United Irishmen had early identified the Defenders as potential allies and leading members such as James Hope had regularly travelled throughout the country organising cells and distributing propaganda such as the Northern Star newspaper.
The Defenders of County Down withdrew support before the United Irish defeat at the Battle of Ballynahinch on 12 June 1798, as their leader John Magennis had received good local information on the size and placing of the British forces.