Michael Gale (pictured right) and the victim, Steve Edwards, had a history of animosity towards each other when they got into an argument outside the clinic on the morning of May 4 over Edwards' assault on an elderly woman in 2017.

Gale told Edwards "this is for hitting the old lady" and punched him in the face, prompting the two men to get into a physical fight.

At one stage, Gale saw a knife on the ground and, believing it belonged to Edwards, picked it up and stabbed him in the chest. Edwards began bleeding profusely and fell to the ground.

Gale was heard saying " he was just a f--king dog, who cares" as he walked away before getting on his push bike and riding off.

Edwards was taken to hospital but could not be saved.

Gale was arrested four days later and charged with murder. The knife was never recovered.

He had been due to stand trial in the NSW Supreme Court in February however pleaded guilty to the reduced charge of manslaughter by reason of excessive self-defence in a plea deal with prosecutors.

In sentencing Gale on Friday, Justice Mark Ierace found the 54-year-old had not intended to kill Edwards that day, only cause him grievous bodily harm.

He noted Gale had had a deprived childhood marred by violence and developed an addiction to heroin at 16.

"I accept [the psychologist's] analysis that the offender's psychological profile, as shaped by his negative life experiences, and his poor ability to regulate negative emotions, were contributory factors in the commission of the offence," Justice Ierace said.

However, he also noted Gale had a lengthy criminal history which included knife offences and the malicious wounding of a man he stabbed in the back of the head.

Justice Ierace set a non-parole period of eight years, meaning with time served, Gale will be eligible to apply for parole in 2026.