His breakthrough in speed skating reached Andersen as he prepares for the 1500 meters for the Norwegian team for the 1948 Olympic Games qualifying in 1948 in St. Moritz. He started but then at the Olympic Games in the 10,000 meters, because he was not nominated for the 1500 meters. The then 10,000 - meter race but was canceled due to poor ice conditions.
From 1950 to 1952 Andersen was the world's best speed skaters and won the world title three times and just as often the European Championship. At the 1952 Olympics in Oslo, he won over 1500 meters, 5000 meters and 10,000 meters.
After the Olympics in Oslo, he resigned first, and then in 1954 to return to the European Championships, where he won silver. At the Olympic Games in 1956, he finished sixth in the 10,000 meters and was the eleventh over 5000 meters.
During his career, he set five world records and was the first 10,000 meters in 17 minutes.
Andersen led the Peerage 1952-1954 on for 708 days. Its maximum value was 187.446 points.
In 1952 he won the election to Norway's Sportsman of the Year and the first endowed Fearnleys olympiske ærespris, 1949 Morgenbladet gold medal.