Liddell debuted for Scotland in a 5–4 wartime win over England at Hampden Park, equalising Tommy Lawton's opening goal. He gained several more wartime caps. He gained his first full cap against Switzerland scoring twice in a 3–1 win at Hampden Park on 15 May 1946 At international level, Liddell played predominantly as an outside left, in competition with Scotland-based Lawrie Reilly and Willie Ormond. The Scottish Football Association (SFA) denied Liddell and his teammates the opportunity to participate in the 1950 World Cup, hosted by Brazil, because of an earlier decision not to sanction involvement as British Home Championship runners-up. The decision meant qualification depended on the final match against England on 25 May 1950, which Scotland lost 1-0 when joint-first needed only a draw. Despite pressure from players, the SFA maintained its position.