Retired midwife Ann Geddes, 63, was found dead at the Angus home she shared with her husband on Sunday February 7 this year.
Roger Geddes, 61, was originally accused of murder but prosecutors have accepted his plea of guilty to the lesser charge of culpable homicide on the grounds of diminished responsibility. Experts who examined the retired civil servant concluded he was mentally impaired at the time.
The couple's daughter, Angela Geddes, previously claimed that prosecutors had let her "cold and calculating" father "get away with murder".
Judge Lord Doherty at the High Court in Edinburgh made Geddes the subject of a compulsion order and a restriction order without limit of time.
The move means Geddes, who has been detained at the State Hospital in Carstairs since February, will remain there until the authorities feel he is well enough and able to be released.