 In 1997 Muldoon and Derry won the Ulster Under-21 and All-Ireland Under-21 Football Championships, defeating Fermanagh and Meath in the respective finals.Muldoon was also on the team the following year, but Derry were defeated at the Ulster final stage by Armagh.He made his Derry Senior debut in the 1997 season and reached the Ulster final, where they were beat by Cavan.