Canberra's oldest killer will die in custody after he was sentenced to nine years in jail for the murder of his wife by the ACT Supreme Court today.

Donald Morley, 93, pleaded guilty after suffocating Jean Morley, 92, in her bed in July last year.

It was the last act in a marriage which had lasted 69 years.

The pair had been teenage sweet hearts.

Today Justice David Mossop said the couple had lived "the Canberra dream" arriving from England in 1970, where they lived a prosperous and happy life.

Morley was a master tooler at the Royal Australian Mint, and Jean Morley worked for an accountant.

The pair had no children, but owned their own home and led a full social life, which included regular lunches with close friends.

Justice Mossop told the court today it was after the couple went out for lunch with friends that the crime occurred.

He said Jean Morley had told her husband she hadn't enjoyed the outing, and he'd agreed with her.

Mrs Morley had been suffering dementia and Morley himself had declining health at the time.

The court heard he told a community worker "we've lived too long".

Morley told police he had gone to bed that night before his wife, and that was when he decided to end both their lives.

Morley had told the court that when Jean Morley came to bed he suffocated her, and then made three attempts to kill himself.

The crime was discovered later by a health worker.

"That's my angel," Morley told the woman about Mrs Morley, before police and ambulance officers arrived.

'Murder remains murder'

Justice Mossop said Morley was not motivated by malice, and noted a doctor's assessment that with both declining in health and Morley struggling to care for his wife he had "been unable to see a way through".

That was despite discussions about home care packages and other help available to the pair.

"[Morley] came to fear the future and believed that this was an acceptable option," Justice Mossop said.

But he said that did nothing to diminish the crime.

"Murder remains murder, notwithstanding the age or infirmity of the victim or the perpetrator," Justice Mossop said.

Justice Mossop acknowledged that punishment was not a large consideration, but general deterrence was a factor.

"The forceful murder of one's spouse must be denounced," he said.

The court had earlier heard Morley has between three and six months to live.

He watched today's sentencing via video link in a hospice where he is being treated for terminal cancer.

But he refused to suspend the sentence, saying that would fail to recognise the gravity of the crime.

Morley was sentenced to nine years in jail with a non parole period of four-and-a-half years.