 He first represented Australia in rugby league at age 30 in 1958 in the first Test against the touring Great Britain side at the Sydney Cricket Ground, an appearance in which he became Australia's 25th dual code rugby international, following Ken Kearney (a team mate that day playing hooker) and preceding Arthur Summons.He scored a try on début as the Australian's defeated the tourists 25-8.Mossop then played in the remaining Ashes Tests though the Lions would go on to win the remaining games and the series 2-1.