The discovery was made shortly after midday on the railway tracks at platform eight on the low level of Glasgow Queen Street station on Saturday.
Officers are treating his death as unexplained and his relatives have been informed.
Police believe he may have fallen from the bridge on Dundas Street but would like to trace his last movements and establish the circumstances surrounding his death.
The line takes in Helensburgh, Milngavie, parts of Lanarkshire and Edinburgh. The west entrance to the station is on Dundas Street.
Detective Sergeant Nicola Phillips, of the British Transport Police (BTP), said: "The man was last seen on CCTV leaving the station around 11.35pm on Friday, January 4, and it is not entirely clear how he came to be on the tracks.
"I am, therefore, appealing for anyone who has any information which can help us piece together his movements between Friday night, and when his body was discovered, to contact BTP as a matter of urgency."