Nils Opdahl was a member of the Norwegian men’s gymnastics team, which won an Olympic gold medal in the all-around free system event. His younger brother Jacob was also a member of the victorious Norwegian gymnastics team.
Nils started his professional career as a clerk. After his vocational education, he went to the United States for some time. Back in Norway at the time of the 1912 Olympics, he followed his father’s footsteps and became a sausage maker and butcher. In the early 1920s he was a merchant. In 1912, he married Augusta Henrikke Johansen; they had a son and a daughter.