Arto Tiainen made his international début at the 1956 Winter Olympics, where he was 26th at 15 km. At the 1958 World Championships he won bronze in the relay, was fourth at 50 km, fifth at 30 km and 12th over 15 km. Tiainen competed in both the 1960 Winter Olympics and 1962 World Championships, but not very successfully, placing 18th in the 30 km at Squaw Valley, and fourth in the 50 km at the World Championships. At the 1964 Winter Olympics Tiainen won bronze in the 50 km and then added a silver in the relay, also placing 13th in the 30K at Innsbruck. Tiainen won his last international championship medal at the 1966 World Championships, where he won silver in the 50 km and made his last international appearance at the 1968 Winter Olympics, where he was 16th in the 30 km. Tiainen also won the 50 km at 1959 and 1960 Lahti Ski Games, won the 30 km at the 1959 Swedish Ski Games in Falun, and won the 50K at Holmenkollen in 1964 and 1965, also being awarded the Holmenkollen medal in 1965. Domestically Tiainen won eleven Finnish titles – one at 15 km (1958), three at 30 km (1960-61, 1963), four over 50 km (1960, 1962-63, 1968) and three in the relay (1957, 1962, 1965). During and after his sporting career Tiainen worked as a police constable in Kuopio and Mikkeli, while from 1968-72 he also worked as a head coach of the Finnish national cross-country skiing team. In 1970 Tiainen served for two months in the Finnish Parliament (Eduskunta) as a representative of Mikkeli municipality, and later worked as a sporting goods retailer.