Key Digital Collections of Primary Sources related to Irish and Northern Irish History:
Virtual Trinity Library (Ireland) collections, including the archives of famous Irish literary figures and more https://www.tcd.ie/virtual-trinity-library/
Digital Repository of Ireland, browse by collection. https://repository.dri.ie/catalog?mode=collections&search_field=all_fields
CELT, an important collection of digitized primary sources relating to Irish history, literature, culture and politics https://celt.ucc.ie/index.html
See for example the complete digitized works of Irish nationalist Pádraig Pearse https://celt.ucc.ie/pearse.html
Northern Ireland Archives online, including digital access to the Londonderry (British colony) Company Archives https://www.nidirect.gov.uk/information-and-services/public-record-office-northern-ireland-proni/search-archives-online
Irish Script on Screen, a digital collection of 450+ manuscripts, although most are from before the 19th century https://www.isos.dias.ie/index.html
University College Dublin (Ireland) Digital Archives, includes many relevant primary source collections http://digital.ucd.ie/
For example, the 19th century social movements pamphlets collection http://digital.ucd.ie/view/ivrla:45000
And the Roger Casement collection http://digital.ucd.ie/view/ivrla:7150
Chief Secretary’s Office Registered Papers (papers of the British official responsible for Ireland) https://csorp.nationalarchives.ie/
Great Hunger Museum Online Database, which documents the 19th century famine in Ireland, includes many primary sources https://repository.quinnipiac.edu/collections/home.do
1916 Easter Rising: Personalities and Perspectives project, documented related to the 1916 Rising in Ireland, which eventually led to Irish independence http://www.nli.ie/1916/index.html
Letters 1916-1923 Project, digitization project that you can participate in. contains letters relating to the Rising, WWI, Civil War and War of Independence, among other topics https://letters1916.ie/
Bureau of Military History Digital Archives (from 1913-1921) about the revolution in Ireland. Includes photos, witness statements, etc. Via Defence Forces Ireland https://www.militaryarchives.ie/collections/online-collections/bureau-of-military-history-1913-1921
CAIN Archives about conflict (The “Troubles”) in Northern Ireland, from 1968 to the present, via Ulster University https://cain.ulster.ac.uk/index.html
Documents on Irish Foreign Policy, 1919-1951 https://www.difp.ie/
Irish Left Archive, documents related to the political left starting in the early 20th century. Includes historical documents and personal accounts https://www.leftarchive.ie/
Report of the Bloody Sunday Inquiry, 1998 https://webarchive.nationalarchives.gov.uk/ukgwa/20101015151735/http://www.bloody-sunday-inquiry.org/