Crews were called to the scene, a two-story apartment building in the 10500 block of Greenwood Avenue North, at about 3:30 a.m., said Kyle Moore of the Seattle Fire Department.
When firefighters arrived, they found heavy black smoke pouring from the bottom floor unit of the building.
Witnesses told crews that one man was believed to be still inside, and as firefighters entered the unit they found smoke and flames rolling through the apartment, which was piled shoulder-high with combustible materials.
About 10 feet from the door, crews found a man dead on the floor. He was pulled from the unit, and firefighters continued to battle the blaze.
Another man in the unit above was also treated for smoke inhalation.
It took crews about half-an-hour to completely extinguish the flames, Moore said.
An investigation later found that the blaze was accidental, triggered by a pinched electrical cord in the unit.