The incident occurred at about 4:45 a.m. at the State and Lake subway station.
Police said the man was on the platform when he went onto the tracks and made contact with the third rail. He was pronounced dead at the scene.
No other injuries were reported and CPD is conducting a death investigation.
The incident caused the CTA to reroute Red Line trains to the elevated tracks before later resuming around 6:30 a.m.