Casey played at the 2001 World Youth Championship in Argentina and then graduated to the senior United States national team, getting his first cap on March 31, 2004, against Poland. On July 7, 2005, Casey suffered a tear to his ACL while playing against Cuba in the U.S.'s opening game of the Gold Cup. He served as a late sub for the United States during several matches in the 2009 Confederations Cup. Casey scored twice (his first ever Senior team goals) against Honduras in a critical world cup qualifier at San Pedro Sula, Honduras, on October 10, 2009. The unanimous Man of the Match, Casey scored the U.S.'s first two goals, and was fouled to set up the game-winning free-kick goal by Landon Donovan. The win put the United States through to the 2010 World Cup.