Police Officers responded to reports of two people in Penarth Marina shortly after 10pm on Friday 12th October.
They were both recused by colleagues from Penarth Coastguard and South Wales Fire and Rescue Service and were taken to the University Hospital of Wales, Cardiff.
The man, 32, from Penarth died a short while later. The woman, 35, also from the Penarth area was released from hospital with no injuries.
Next of kin have been informed.
The death is not being treated as suspicious, however officers would urge anyone who may have seen the couple walking in the vicinity of the marina at around 10pm to contact us via 101 quoting reference number: 1800389640