Already a member of the Labour Party, Young joined the Scottish National Party (SNP) in 1938, serving as Chair of the SNP in Aberdeen during the 1940s. The SNP was pledged to oppose conscription, except by a Scottish government, and Young refused to register either for military service or as a conscientious objector during World War II. He served two terms in prison, reading Greek as much as possible in his cell. At trial, Young contested the authority of the British government, specifically whether the Act of Union could be used to compel Scots to serve in the British military outside the British Isles. He was convicted under the National Service (Armed Forces) Act 1939 at the Glasgow Sheriff Court in April 1942. He appealed at the High Court in July 1942 but this was dismissed. Young's activities were popularly vilified as undermining the British war effort against the Nazis. His daughter later claimed that he had volunteered in 1939, and was unfit due to a heart problem.