Utriainen was born in Nokia, Finland on 5 February 1991. Her father, Esa Utriainen, was Finnish champion in men's javelin throw in 1979 and represented Finland at the 1983 World Championships. Sanni Utriainen first broke 50 metres in 2008, throwing 51.89 m at the Pihtipudas Javelin Carnival and winning the Finnish youth championship with 51.00 m. In 2009, she placed ninth at the European Junior Championships in Novi Sad, throwing 51.25 m in the qualification and 48.45 m in the final.