During the Second World War, the British occupied the Danish Faroe Islands following Nazi Germany's invasion of Denmark, with Mason serving as the British Consul to the Faroe Islands. He married a local woman, Karen Rorholm. They subsequently left the Faroe Islands. In 1943, he was appointed British Consul in Colón, Panama. He would later, as Sir Frederick Mason CMG, become British Ambassador to Chile (1966-1970) and finally British Permanent Representative to the Geneva Office of the United Nations (1971-1973).