South Yorkshire Police said the discovery was made at an address in the Worsbrough area of the town.
Ambulance staff had called officers to Mayfield Crescent just before 9.40am.
A police spokesman said the body of a 30-year-old man was found at the property.
"At this time, the cause of death is not known and a forensic post-mortem is expected to be carried out later this evening," he said.
"A 27-year-old woman who was also at the property has been arrested on suspicion of murder and currently remains in police custody.
"Officers remain in the area carrying out enquiries to ascertain the exact circumstances surrounding the man’s death."
Anyone with information is asked to call 101, quoting incident number 262 of 25 December 2017.
Information can also be passed on anonymously via the charity Crimestoppers on 0800 555 111.