James Hook played for his country at U19 and U21 levels. Hook played for Wales Sevens team in the Melbourne Commonwealth Games in January 2006. 

He made his Wales Senior Debut in June 2006 on the tour to Argentina playing in the two tests. 

Following his success in the sevens set-up and on the Argentine tour, Hook received inclusion in Wales's squad for the 2006 Invesco Perpetual Series. He replaced the injured Welsh Captain Stephen Jones in the first game of the Series against Australia and demonstrated the confidence and composure to guarantee further first-team appearances. 

Hook represented Wales in the 2007 RBS Six Nations against Ireland, Scotland, France and Italy. He starred in the last match of the tournament against England and produced a man-of-the-match performance. 

Hook received a call-up to Wales's two-Test tour to Australia in May 2007; he started at fly half for the first Test in Sydney, scoring two conversions, two penalties and a drop goal. He also appeared for Wales in the second Test loss in Brisbane and in June was announced in Gareth Jenkins's 41-man preliminary Rugby World Cup 2007 summer training squad, making the final cut in August to be included in the Rugby World Cup Squad. 

Hook was included in Warren Gatland's Grand Slam winning RBS Six Nations side in 2008. The fly half made two substitute appearances against Italy and Ireland, at the Triple Crown winning clash at Croke Park, and scored 44 points during the tournament including a superb try score against Scotland at the Millennium Stadium.

He showed his versatility on the summer tour to South Africa, playing the second Test in the unaccustomed position of full-back.

He came on as a replacement against the Springboks in the opening clash in the autumn, banging over four penalties in a narrow defeat. Hook started against Canada and came on as a replacement against New Zealand.