Witnessess said the 33-year-old man appeared to be under the influence of drugs when a row erupted on Sunday on a training linking Delhi to the city of Amristar.
Male relatives of the pregnant woman attacked the man who was found bleeding and unconscious on the platform of the Karnal train station in Haryana state.
He was taken to a hosptal in Chandigarh, but never regained consciousness.
Police say an investigation has been launched and the train’s ticket collector arrested for failing to inform the authorities about the incident.
Police say a blood sample was taken from the victim to verify whether he was on drugs.