 Cathcart was called up to the Northern Ireland squad in May 2009, along with nine other uncapped players for the international friendly against Italy on 6 June.Cathcart made his full international debut in Northern Ireland's 1–0 win against Slovenia in Maribor on 3 September 2010.Playing out of position at left-back, due to an injury to Jonny Evans, Cathcart put in a strong performance and set up the winning goal for Corry Evans.