An elderly Perth man has pleaded guilty to murdering his sick partner in a mercy killing.

Herbert Bernard Erickson, 81, smothered his disabled partner Julie Kuhn with a pillow at their home in Armadale in January.

He then killed his two dogs and inflicted severe burns on his hands when he tried to electrocute himself.

Ms Kuhn suffered from a severe form of paralysis and was confined to a wheelchair.

A previous court was told the couple had a pact.

Erickson's bail has been renewed until he is sentenced in January.

Outside the court, his lawyer David Manera says he will be arguing that his client should not receive a life jail term.

He says the circumstances of the case are exceptional.

"This was an offence committed not for any gain by Mr Erickson," he said.

"He dearly and deeply loved his partner and it is not a situation where he stood to gain anything.

"He made a genuine attempt thereafter to take his own life."

Erickson says he hopes the court will show him mercy.

"I don't want to go to jail," he said.

"I want to be with my partner really but I'm still here, worse luck."