Koskela was born in Virolahti on 31 March 1921. He began his athletic career in the field of cross-country skiing, in which he won a national under-18 event in 1938. Inspired by the Finnish success in long-distance running at the 1936 Summer Olympics, however, he decided to pursue athletics as his sport of choice. His career was interrupted by World War II, during which time he served for his native Finland in the Gulf of Finland and around the Svir River. As a result, his first major competition did not come until the 1945 Kaleva Games in Turku, where he finished fourth in the 5000 metres event as a member of Virolahden Sampo. Despite winning the following year, however, he was not selected to represent Finland at the 1946 European Athletics Championships.