Valdez has represented Paraguay at the 2006 and 2010 FIFA World Cup tournaments, he also participated at the 2004, 2011 and 2015 Copa América tournaments; in 2011 Paraguay finished runners-up. Valdez has made over 70 national team appearances and scored 13 goals, with one of his goals coming in a 1–0 historic victory against rivals Argentina on 9 September 2009 which secured Paraguay's qualification to the 2010 World Cup and the result being Paraguay's second official victory against Argentina.