The Blue Line service was temporarily suspended between Jefferson Park and California on Sunday morning after a medical emergency on the tracks, according to a CTA alert.
The Chicago Fire Department confirmed the death of one person and two others were transported to a hospital.
The CTA site said that shuttle buses were available between Jefferson Park and California stops and Commuters were encouraged to use the No. 56 Milwaukee bus as an alternate service for those affected.
The transit service said it is working to restore normal service as quickly as possible.