Harte made his senior debut for Ireland in August 2006 in a Celtic Cup game against France. Harte's brother, Conor, and his sister, Emer, also made their senior international debuts on the same day. Harte was a member of the Ireland teams that won the 2009 Men's EuroHockey Nations Trophy and the 2011 Men's Hockey Champions Challenge II. He also helped Ireland win Men's FIH Hockey World League tournaments in 2012, 2015 and 2017. He has captained the Ireland team since 2015. In 2015 Harte was named Goalkeeper of the Tournament at the World League Round 2, the World League Semifinals and the Men's EuroHockey Nations Championship. Along the way he helped Ireland qualify for the 2016 Summer Olympics and win the bronze medal at the 2015 EuroHockey Championships. He was subsequently named FIH Goalkeeper of the Year for the first time. He won the award for a second time in 2016. In June 2017 Harte was a member of the Ireland team that won the Hamburg Masters, defeating Germany 4–2 in the final.