A husband is thought to have strangled his wife then hanged himself, police have said.
Ambulance crews fought in vain to save the woman, aged in her 60s, and the body of the man, also in his 60s, was found elsewhere in the flat.
The drama happened at a property in Rugby Street, Bloomsbury, central London, Scotland Yard said.
A Yard spokesman said it was a murder investigation but at this early stage officers are not looking for anyone else in connection with the deaths.
Police were called by London Ambulance Service to the flat in Rugby Street, shortly before 1.45pm on Wednesday, following reports that a woman had been found injured.
The woman was treated at the scene following an apparent assault but was pronounced dead at 2.10pm.
The man was pronounced dead one minute later.
The deceased are a husband and wife and next of kin are aware.
Post-mortem examinations took place on Thursday at St Pancras Mortuary and gave the causes of death as strangulation for the woman and injuries consistent with hanging for the man.