Kim Borg was born in Helsinki. He studied voice with Heikki Teittinen at the Sibelius Academy (1936–1941 and 1945–1947), where he also received training in theory and composition with Leo Funtek and Aarre Merikanto, and then pursued vocal studies with Andrejewa de Skilondz in Stockholm (1950–1959). He also studied biochemistry at the Helsinki University of Technology, and received a diploma in 1946. In 1947 he made his formal concert debut in Helsinki, and in 1951 his formal operatic debut in Århus as Colline in La bohème. In addition to his concert appearances, he sang regularly in opera in Helsinki and Copenhagen (1952–1970), Stockholm (1963–1975), and Hamburg (1964–1970). In October 1959 he made his Metropolitan Opera debut in New York City as Count Almaviva, remaining on its roster until 1962. In 1961 he appeared as Boris Godunov in Moscow.