Wallace Howard was determined to protect his only daughter when he shot dead a man facing armed robbery charges, a court has heard.

Howard was 64, 160 centimetres tall and walked with a limp because of a leg injury when he went with his daughter to the Preston home of the powerfully built Mathew Schmidt, 35.

Howard was armed with a loaded handgun and shot Mr Schmidt once in the abdomen during a confrontation on Saturday, February 25 last year. Mr Schmidt died in hospital.

Howard has pleaded guilty to one count of manslaughter.

Defence barrister Wayne Toohey told the Victorian Supreme Court on Monday that Howard's daughter, Samantha, now aged 41, had been attacked the night before by Mr Schmidt and his wife Karen.

She had gone to the Schmidts' home after her partner, Jamie Morgan, had been arrested. Morgan had been an associate of the Schmidts.

Mr Toohey said Ms Howard was beaten by the Schmidts and Mr Schmidt threatened her with a knife before she fled the house, leaving behind her handbag.

Ms Howard stayed the night with her parents and told them what had happened and that she needed to go back to the Schmidts' house to retrieve her handbag.

It contained important paperwork she needed to be able to visit her partner in prison.

Howard did not want his daughter to go alone to the Schmidts and she wanted him to be with her.

Mr Toohey said Howard had known Mr Schmidt was facing charges over two armed robberies at a liquor store and a post office where firearms were allegedly used.

Mr Toohey said Mr Schmidt was known to have a violent temper and was a 180 centimetre tall, powerfully built man while Howard had a pot belly and suffered chronic pain from a back injury.

"He (Howard) was certainly no physical match for the deceased [Mr Schmidt] in any way, shape or form," Mr Toohey said.

Howard and his daughter went to the Schmidts' home just before noon on the Saturday and called out for Mrs Schmidt to bring out the handbag.

Mr Toohey said Howard's reasoning in taking a loaded handgun with him was that if Mr Schmidt threatened him and his daughter, he would pull out the pistol to scare him.

If the gun did not force Mr Schmidt to back away, Howard planned to fire it into the air.

But Mr Toohey said things happened very quickly and, as Mr Schmidt began walking towards him, in a moment of panic Howard fired in his direction before driving off.

Schmidt turned to his wife laughing and said, 'The dog shot me", then collapsed.

Mr Toohey said Howard admitted that firing the gun was unlawful and dangerous but he never intended to kill Mr Schmidt.

In her victim impact statement, Mrs Schmidt said she was haunted every night by the memory of what had happened to her husband.

She said Mr Schmidt called out to her to hold him after he had been shot and his last words were, "I love you so much".

She saw a tear run down his cheek as he lost consciousness.

The plea hearing before Justice Cameron Macaulay continues.