Karen’s first public skating appearance was as a “snowflake” in a winter carnival at age six. She went on to become the third Canadian woman to win the World Amateur Skating title (Barbara Ann Scott won in 1947 and 1948, and Petra Burka in 1965). Karen was also inducted into the Canadian Amateur Athletic Hall of Fame and the Canadian Sports Hall of Fame.
Between 1961 and 1965, Karen captured first place in numerous provincial competitions including BC Invitational, BC Section Junior, and Senior Ladies, and BC Coast Free Skating. She was the 1965 Canadian Junior Ladies Champion, and five-time Canadian Junior Champion (1968, 1970, 1971, 1972, 1973), and she won two silvers in 1967 and 1969 in the same event.
Karen competed at four World Championships between 1967-1970, placing 12th, 7th and 4th, but had to withdraw from the 1969 competition due to stress fractures in both legs. She made it to the semi-finals (placed 7th) at the 1968 Winter Olympic Games in Grenoble, France, and won silver at the 1969 North American Senior Ladies Championships in Berkeley, Ca. (1st in figures).
In 1971 she won the North American Championships in Peterborough, Ontario. At the 1971 World Championships in Lyon, France, she won the bronze and the next year won the silver in Calgary. As a Silver medalist at the 1972 Winter Olympic Games in Sapporo, Japan, she was only Canadian to win a medal. Karen Magnussen won gold at the 1973 World Championships in Bratislava, Czechoslovakia and was first in all three categories: overall, freestyle and compulsory figures.