She first competed in the Olympic Winter Games in 1948, when she was eighteen years old, where she earned a bronze medal behind Barbara Ann Scott of Canada and Eva Pawlik of Austria.
Just eight days before the 1952 Olympic Games, she defended her European championship title. At the Oslo Games, Altwegg built a huge lead during the compulsory figures and then held on to win the gold medal despite placing fourth in the free-skating, as she earned the overall first-place votes of six of the nine judges
As an Olympic champion, Jeannette was offered large sums of money to turn professional and perform in ice shows. Instead she retired from skating, moved to Switzerland and took a low-salary job working with war orphans.