Magnar Estenstad was born in the former municipality of Hølonda in neighborhood of Trondheim, which later fostered famous skiers like Toralf Engan and Oddvar Brå. Estenstad and Brå are the Norwegian skiers with most championships at 50 km, with five each. Estenstad’s first in 1948 came as a surprise. On almost home ground in Trondheim, a few weeks after the 1948 Olympics, the 23-year-old newcomer won with a margin of over three minutes. He later defended his title in 1949, 1952, 1953 and 1954. In 1950 he was national champion in 30 km, and competed in the World Championships in Lake Placid the same season, where he placed seventh at 50 km. At the 1952 Oslo Olympics he came third at the 50 km and the relay, in which he skied the first leg. Estenstad won the 50 km in Holmenkollen at the end of the season, his only Holmenkollen victory.
In 1954 Estenstad had a great start to his season, winning the Norwegian 50 km championship with a four minute margin. He was also a member of the winning relay team for his club Leik. The last event in the national championships was the 30 km race. He was in a clear lead when he fell and broke his thigh bone (femur) only one kilometer from the finish. Instead of going to the World Championships in Falun, he went to hospital where he stayed for five months. When he came home from the hospital, the broken leg was much shorter than the other one, and he was forced to end his skiing career at the age of 29. Magnar Estenstad was a farmer, and died in his home community in 2004, aged 79.