The Leonhard Seppala Humanitarian Award, which honors excellence in sled dog care, is named in honour of him.

[5][6] He was the eldest child of Isak Isaksen Seppälä (Tornedalian born in Sweden) and Anne Henrikke Henriksdatter.

[4][10] When Seppala was two years old, his family moved within Troms county to the nearby the island of Skjervøya in Skjervøy Municipality.

His friend Jafet Lindeberg had returned from Alaska and convinced Seppala to come to work for his mining company in Nome.

Lindeberg, his friend and supervisor at Pioneer Mining Company, had brought the puppies from Siberia as a gift for the explorer Roald Amundsen, whom he hoped would use them for his upcoming expedition to the North Pole.

Indeed, when the whiteout conditions suddenly lifted, Seppala found that he and his team were at the bottom of a hill, racing towards the cliffs along the sea.

Seppala felt he had abused the dogs' loyalty by putting them in danger of death and injury, and withdrew from the race in shame.

A relay of respected mushers was organized to expedite the delivery, and Seppala (with lead dog Togo) was chosen for the most forbidding part of the trail.

Seppala's section of trail featured a dangerous shortcut across Norton Sound, which could save a full day of travel.

A sustained east wind could also push the ice out to sea, and a team caught on a drifting floe could find itself stranded on open water.

Seppala had taken the shortcut across the Sound several times in his career; a less-experienced musher was likelier to lose not only his life and the lives of his dogs, but also the urgently needed serum.

[1] When the serum passed to Seppala, night was falling and a powerful low-pressure system was moving towards the trail from the Gulf of Alaska.

Seppala had to decide whether to risk Norton Sound in high winds in the dark, when he could not see or hear potential warning signs from the ice.

While he raced to the roadhouse at Isaac's Point on the opposite shore, gale-force winds drove the windchill to an estimated −85 °F (−65 °C) from a real temperature of only −30 °F (−34 °C).

When he arrived there at 8 pm, his dogs were exhausted; they had run 84 miles (135 km) that day, much of it against the wind and in brutal cold.

[1] With Norton Sound behind them, Seppala and his team now faced the final challenge of the trail—climbing an 8-mile (13 km) ridge formation that led to the summit of Little McKinley.

The trail here was exposed and the steep grade grueling for the dogs, who were sleep-deprived and had already raced 260 miles (420 km) over the previous 4.5 days.

Despite a series of time-consuming mishaps on the trail, Seppala won the race against the bigger, slower dogs driven by Walden and his followers.

The enthusiasm for sled dog racing in New England together with the Serum Run publicity and the victory over Walden made it possible for Seppala and partner Elizabeth Ricker to establish a Siberian kennel at Poland Spring.

In 1961, Seppala revisited Fairbanks and other places in Alaska at the invitation of American journalist Lowell Thomas, enjoying a warm reception from the Alaskan people.