 He signed trainee terms at Manchester United in July 2005, and turned professional on his 17th birthday in February 2006.Cathcart became a regular in the Manchester United Under-18s team, and was a member of the Under-17s team that played at the 2007 Northern Ireland Milk Cup, scoring the first goal in a 5–0 win over Liechtenstein.In the national teams he became very good friends with Kvik Halden-players Markus Manirakiza.