Partai Unionis Demokrat bermula dari Partai Unionis Protestan dan secara historis memiliki hubungna yang kuat dengan Gereja Presbiterian Bebas di Ulster. Selama The Troubles, DUP menentang pembagian kekuasaan dengan para Nasionalis ataupun Republikanis Irlandia sebagai sebuah cara untuk menghentikan konflik. DUP berkampanye menentang Perjanjian Sunningdale tahun 1973, Perjanjian Anglo-Irlandia tahun 1985, dan Perjanjian Jumat Agung tahun 1998. Pada tahun 1980-an, DUP terlibat dalam pembentukan gerakan paramiliter loyalis Third Force[20][21][22] dan Ulster Resistance[23], yang terakhir adalah membantu menyelundupkan sejumlah besar senjata ke Irlandia Utara.[24]
^ abcNordsieck, Wolfram (2017). "Northern Ireland/UK". Parties and Elections in Europe. Diarsipkan dari versi aslinya tanggal 7 November 2016. Diakses tanggal 28 September 2018.
^Jamie Merrill (9 June 2017). "What is the DUP position on Brexit?". The Essential Daily Briefing. iNews. Diarsipkan dari versi aslinya tanggal 16 August 2017. Diakses tanggal 16 June 2017. No-one wants to see a 'hard' Brexit, what we want to see is a workable plan to leave the European Union, and that's what the national vote was about – therefore we need to get on with that.
^Unionism and Orangeism in Northern Ireland Since 1945. Belfast: Blackstaff Press. hlm. 199. The men on the Antrim hillside became the nucleus of a paramilitary formation 'The Third Force' which would play a role in what the DUP called 'The Carson Trail'
^Wood, Ian S. (2006). Crimes of Loyalty: A History of the UDA. Edinburgh University Press. hlm. 74. ISBN978-0748624270. Dr Ian Paisley, who had been close to Bradford, called for tax and rent strikes by Loyalists and announced the formation of a new paramilitary body for which he claimed he was helping to recruit. Because it was to supplement the RUC and UDR, he called it the 'Third Force'