Rubuta ci gaba don wannan sakin layi - Horan ya fara buga wasan kasa da kasa a kan Amurka a lokacin kakar 1999-00, amma bai sake samun nasara ba har zuwa kakar 2002-03, wanda ya zo da Fiji. Ya rasa matsayinsa ga Reggie Corrigan a lokacin gasar Rugby ta Duniya ta 2003 da kuma gasar zakarun kasashe shida ta 2004 da 2005, amma ci gaba da yin rawar gani ga Munster ya gan shi ya sake samun matsayinsa a cikin tawagar. Ya rike matsayinsa na 2006
, 2007, 2008 da 2009 Gasar Kasashe shida, farawa kowane wasa na kamfen din Grand Slam na nasara na Ireland. Ya kuma kasance wani ɓangare na tawagar Eddie O'Sullivan ta 2007 Rugby World Cup. Ya rasa Gwajin Nuwamba na 2009 bayan ya yi aikin tiyata na zuciya, kuma ya rasa matsayinsa ga Cian Healy, wanda ya riƙe matsayin loosehead-prop a lokacin Gasar Cin Kofin Kasashe shida ta 2010. Horan ya buga wasa da Barbarians F.C. da New Zealand Maori a lokacin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Wasannin Ya rasa gasar zakarun kasashe shida ta 2011, amma an zaba shi a cikin tawagar horar da 'yan wasan Ireland na gasar cin kofin duniya ta Rugby ta 2011 a watan Agusta 2011. Ya buga wa Scotland wasa, amma ya rasa zabinsa a cikin 'yan wasan karshe na gasar cin kofin duniya.