The man, who is in his 50s, was hit by a southbound train while attempting to cross the tracks near the Rainier Beach station at roughly 5 p.m.
The man was taken to Harborview Medical Center with what are being described as "heavy trauma life-threatening injuries," according to the Seattle Fire Department. When medics arrived on scene, the man had a pulse but was unconscious
Central Link light rail service was temporarily interrupted after the crash.
Detectives from the Seattle Police Department's Traffic Investigation Squad are investigating the collision.