Ibunya bernama Maura Gallagher dan ayahnya Bobby Horan.<ref name=autogenerated6>{{cite web|url=http://www.dailyrecord.co.uk/showbiz/celebrity-interviews/2012/04/16/mums-of-one-direction-stars-reveal-how-the-boys-have-grown-into-music-sensations-86908-23826535/ |title=Mums of One Direction stars reveal how the boys have grown into music sensations – The Daily Record |publisher=Dailyrecord.co.uk |date= |accessdate=2012-06-11}}</ref> Dia memiliki seorang kakak laki-laki bernama Greg dan berpacaran dengan Keisha Yehezkiel Mandagi .<ref>{{cite web|url=http://www.unrealitytv.co.uk/x-factor/x-factor-2010-niall-horans-brother-says-one-direction-get-along-well/ |title=X Factor 2010: Niall Horan's brother says One Direction get along well |publisher=Unreality TV |date=6 November 2010 |accessdate=2012-03-17}}</ref> Orang tua nya bercerai saat ia berusia lima tahun. Setelah itu, Horan dan kakaknya hidup berpindah-pindah antara rumah ibu dan rumah ayahnya. Ibunya menikah lagi dengan seorang pria bernama Chris dan pindah ke Edgeworthstown, County Longford.<ref name=autogenerated6 /> Dia bersekolah di Coláiste Mhuire, sebuah sekolah katolik di Irlandia.<ref>{{cite news|url=http://www.westmeathexaminer.ie/news/mullingar/articles/2010/07/07/3998386-mullingar-teen-has-got-the-x-factor/|newspaper=[[Westmeath Examiner]]|title=Mullingar teen has got the X Factor|date=7 July 2010}}</ref><ref name="Glimpse">{{cite news|author=Liz Thomas|url=http://www.dailymail.co.uk/tvshowbiz/article-2121920/Beatlemania-takes-new-Direction-Thousands-gather-Montreal-catch-glimpse-band.html|title=Beatlemania takes a whole new Direction! Thousands gather in Montreal to catch a glimpse of the band|work=Daily Mail |accessdate=2012-03-31|location=London}}</ref>. Di sekolah, Niall bergabung dengan tim paduan suara sekolah yang tampil setiap hari [[Natal]].<ref name="thehothits1">{{cite web|url=http://www.thehothits.com/artists/6069/one-direction/bio |title=One Direction – Biography, Overview, Artist feature, Music, Photo Gallery, News |publisher=Thehothits.com |accessdate= 27 April 2012}}</ref><ref name=autogenerated10>{{cite web|author=South Wales Echo |url=http://www.walesonline.co.uk/showbiz-and-lifestyle/showbiz/2012/01/13/one-direction-prepare-for-cardiff-sell-out-shows-91466-30112196/ |title=One Direction prepare for Cardiff sell-out shows - Showbiz - Lifestyle |publisher=WalesOnline |date=2012-01-13 |accessdate=2012-06-11}}</ref> Horan mulai bermain gitar ketika kakaknya mendapat sebuah gitar di hari Natal tetapi gagal memainkannya, jadi Horan mulai belajar sendiri cara memainkannya dari YouTube.<ref>{{cite web|url=http://www.capitalfm.com/artists/one-direction/news/best-christmas-present/ |title=One Direction, Jessie J and Wretch 32 Unveil Their Best Christmas Presents Ever |publisher=Capital FM |date=21 December 2011 |accessdate=2012-03-17}}</ref>
