When he was 16-years-old Gunnar Sköld began competitive cycling in his hometown of Västerås in Sweden. After achieving some good results Sköld initially stopped competing after getting married in 1918, before making a comeback two years later. On his return he won both the 10 km and 100 km races at the Swedish Championships and earned an opportunity to ride at the World Championships. His hard work paid off as he became the winner of the inaugural amateur road race at the championships. The race was not without incident; just two miles in Sköld had to avoid a log that was thrown into the road by some construction workers. Approaching the end of the race he was then attacked by a large angry dog, but went on to win the race by almost five minutes.
Consistent results then earned Sköld a place on the Swedish Olympic team for the 1924 Games in Paris. He just missed out on a medal in the individual road race, finishing fourth, but won bronze in the combined team event. That same year he then won the one-day classic race Mälaren Runt and retained his title the following year. Once Sköld retired from the sport he became the treasurer and vice-chair of his cycling club Upsala CK.