The son of Christof Frommelt, a cross-country skier who carried Liechtenstein’s flag at the Opening Ceremony of the 1948 Olympic Games, Willi Frommelt first appeared on the Olympic stage as a teenager at Sapporo. Two years later he made a small piece of history by winning a bronze medal in downhill at the 1974 World Championships at St. Moritz as this was the first medal won by a Liechtensteiner at world or Olympic level. He was equally capable at all three disciplines then contested and won an Olympic bronze in slalom in 1976 and a second World Championship medal, this time at giant slalom in 1978. He also awarded a silver medal for his combined performance at slalom and downhill at the 1976 Olympics although, since the combined event was not an Olympic event, this was considered a World Championship medal only. Oddly for a multiple championship medallist he only registered a single podium finish, a third place, in five seasons of World Cup competition.
After retirement from skiing he took a degree in business management and later worked as a financial planner for the Liechtenstein National Bank. Frommelt also moved into politics with the centre-right Fortschrittliche Bürgerpartei in Liechtenstein and served a term as a municipal councillor.
His brother Paul Frommelt followed in Willi’s footsteps and was an Olympic skiing medallist whilst another brother, Peter, represented his country in table tennis.