Marshall, 27, from St Ann Parish in Jamaica is competing in the famous endurance contest, racing 1,850km across Alaska on a sled pulled by a team of dogs.
"Nobody knew about dog sledding in Jamaica," says Marshall, an adventure guide who fell into the sport by accident when his boss asked him to help care for a few sled dogs.
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One thing led to another, and soon Marshall and his company were using the dogs to pull sleds modified with the addition of wheels.
At first, he admits, "I thought it would not work out".
The company, Jamaica Dogsled Team, now offers the wheeled sled rides on the island as a tourist attraction.
Cold weather a challenge
But for Marshall, they were a step to something bigger: training to run a real race in real snow.
It wasn't easy. For one thing, the conditions weren't exactly what he would face in the north.
"The weather was kinda warm, so we were doing it at five o'clock in the morning," he recalls.
Still, the training paid off, and eventually Marshall found himself headed to Canada to race.
He still recalls stepping out of a plane in Whitehorse, in Canada's Yukon Territory. He wasn't wearing gloves.
"All the sudden my finger was all stiff," he laughs.
"I didn't know what I was getting myself into," he adds, on a more serious note. "I didn't know what 18 below (zero) was; I didn't know any of that stuff."
Cool Runnings comparison
Marshall persevered, doing well in smaller races and qualifying for the 2009 Yukon Quest, a 1,600 kilometre race in Alaska and Canada.
Finishing the Quest brought Marshall some media attention - it's tough to resist a story about an athlete from a tropical nation competing in a cold weather event.
And because he's from Jamaica, Marshall inevitably draws comparisons to the island nation's Olympic bobsled team, whose travails and eventual success drew lots of attention, inpiring the 1993 movie Cool Runnings.
"Everybody brings that up," Marshall laughs. In fact, when he first took up the sport, friends teased him asking "Did they make a mistake and write 'dogsled'?" he says.
But all this was just a prelude to his 2010 Iditarod bid.
His trainer this year was Lance Mackey, of Fairbanks, who earlier this week won his fourth consecutive Iditarod in near-record time.
Some of Marshall's Iditarod team even comes from Mackey's kennel.
Finish line looming
Hans Gatt, the second-place finisher, was Marshall's coach before Mackey.
Despite his experience in the Quest and other races in Alaska and Canada, the Iditarod has still proven a challenge, Marshall says.
It's especially windy, and at times "I couldn't see the trail", he says.
Still, he's pushing on, and even moving slowly forward in the pack, at a stage in the race when more than a dozen other mushers have scratched.
Cold and weary, but with less than 270 kilometres to go, Marshall is closing in on his goal.
When he reaches the finishing line at the burled arch in Nome, he'll be the first Jamaican to do so. He'll bask in some well-deserved attention, then head home.
What's the first thing he'll do when he gets there?
"Go to the beach," he laughs.
