[[File:3 Store on Grafton Street, Dublin, Ireland.JPG|thumb|3Store, Grafton Street, Dublin, Irlandia]]
Operasional Three di Irlandia memiliki kode akses 083. Layanan Three di Irlandia diluncurkan pada 26 Juli 2005, sebagai operator keempat di negara ini setelah [[Vodafone Irlandia|Vodafone]], [[O2 Irlandia|O<sub>2</sub>]] dan [[Meteor (operator seluler)|Meteor]]. Jaringan Three yang mencakup 96% penduduk Irlandia (dan 500.000 penggunanya disana) sendiri berbasis pita tunggal 2,100 MHz UMTS.<ref name="insideireland">[http://www.insideireland.ie/index.cfm/section/news/ext/3irelandbroadband002/ 3 Ireland reaches 500,000 customers]{{dead link|date=November 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Three Irlandia sendiri menjalin kerjasama dengan Vodafone dalam sistem ''roaming'' di wilayah tak tercakup Three, dan pada Juli 2012 disepakati kerjasama keduanya dalam pengelolaan infrastruktur. Kerjasama ini membantu Three untuk meluncurkan 4Gnya lebih cepat.<ref>{{cite web|url=http://press.three.ie/press_releases/13-jul-12-vodafone-ireland-and-three-ireland-announce-strategic-partnership-to-share-network-infrastructure/|title=Vodafone Ireland and Three Ireland announce strategic partnership to share network infrastructure|date=13 July 2012|access-date=27 July 2012|archive-url=https://web.archive.org/web/20120716070506/http://press.three.ie/press_releases/13-jul-12-vodafone-ireland-and-three-ireland-announce-strategic-partnership-to-share-network-infrastructure/|archive-date=16 July 2012|url-status=dead}}</ref> Lalu, pada November 2012 hasil lelang menetapkan Three Irlandia sebagai salah satu pemenang jaringan [[LTE]].<ref>{{Cite web |url=http://press.three.ie/press_releases/913/ |title=15-Nov-12 Three welcomes the results of Ireland's spectrum auction. : Media Centre<!-- Bot generated title --> |access-date=21 November 2012 |archive-url=https://web.archive.org/web/20140804161905/http://press.three.ie/press_releases/913/ |archive-date=4 August 2014 |url-status=dead }}</ref> Pada 24 Juni 2013, Hutchison mengakuisisi [[O2 (Irlandia)|O2]] yang dimiliki [[Telefónica]] senilai €780 juta. Operasional O2 kemudian digabungkan dengan Three sehingga penguasaan pasar Three kini sebesar 40%.<ref>[http://businessetc.thejournal.ie/three-buys-o2-mobile-phone-networks-963827-Jun2013/ Three buys O2 and will now control 40 per cent of Ireland's mobile market<!-- Bot generated title -->]</ref><ref>{{Cite web |url=http://pressoffice.telefonica.com/jsp/base.jsp?contenido=%2Fjsp%2Fnotasdeprensa%2Fnotadetalle.jsp&id=0&origen=portada&idm=eng&pais=1&elem=19997 |title=Press Office {{!}} Press Office {{!}} Telefónica<!-- Bot generated title --> |access-date=2022-02-19 |archive-date=2016-01-08 |archive-url=https://web.archive.org/web/20160108070110/http://pressoffice.telefonica.com/jsp/base.jsp?contenido=%2Fjsp%2Fnotasdeprensa%2Fnotadetalle.jsp&id=0&origen=portada&idm=eng&pais=1&elem=19997 |dead-url=yes }}</ref><ref>{{cite web|url=http://www.o2online.ie/o2/uploads/pdfs/press/2013-06-24%20media%20statement.pdf |title=Media Statement |access-date=24 June 2013 |url-status=dead |archive-url=https://web.archive.org/web/20140714215813/http://www.o2online.ie/o2/uploads/pdfs/press/2013-06-24%20media%20statement.pdf |archive-date=14 July 2014 }}</ref> Lalu, pada 27 Januari 2014, Three Irlandia meluncurkan jaringan 4G-nya di Dublin, Cork, Galway, Limerick, Wexford dan Waterford yang kemudian diperluas.<ref>{{cite web |url=http://press.three.ie/press_releases/three-ireland-to-launch-comprehensive-4g-offers/ |title=Three Ireland to launch comprehensive 4G offers |publisher=Hutchison 3 |date=27 January 2014 |access-date=4 February 2014 |archive-url=https://web.archive.org/web/20140221172153/http://press.three.ie/press_releases/three-ireland-to-launch-comprehensive-4g-offers/ |archive-date=21 February 2014 |url-status=dead }}</ref> Setelah merger dengan O2 pada Oktober 2015, pengguna Three mencapai 2 juta.
