Jake Joshua Fenner, 32, has been behind bars since his father, William, died aged 71 at their Darwin home in November 2023.
The pair came to blows after the father refused to drive his son to the airport, with both men sustaining severe injuries to their heads and bodies.
Fenner, who argued he acted in self-defence, was initially charged with murder but that was later downgraded to committing a violent act causing death.
In August 2025, a jury returned a unanimous guilty verdict.
In sentencing in the Supreme Court in Darwin on Friday, Acting Chief Justice Stephen Southwood detailed the father's wounds, including gaping cheek and forehead lacerations and multiple bruises and abrasions.
The trial had heard from a neighbour who saw across his fence a metal pole being raised, then swung down hard during the fight between father and son.
Justice Southwood said an expert witness indicated the father's severe injuries would have prevented him from swimming and he may have already been concussed.
Fenner, who suffered severe lacerations to his scalp during the fight, later pulled his father from the pool, rang triple zero and tried to revive him.
"I find the offender engaged in a violent and sustained attack on the deceased," the judge said, finding the father drowned due to his severe injuries.
The Fenner family was an unhappy one, beset by unpredictable, violent behaviour by the father, Justice Southwood said.
That fed into the son's anti-social behaviour, trouble at school, alcohol and drug abuse and interactions with police, he said.
The younger Fenner was diagnosed with autism spectrum disorder and the jury in the trial heard his father had called him an "autistic c***".
A psychiatrist assessed that Fenner's capacity to appreciate wrongdoing was at least "mildly diminished" by his autism disorder.
Justice Southwood sentenced Fenner to five years' imprisonment, suspended after three years, which means he will be released in November, having already been behind bars for more than two years.
He must abide by strict conditions for two years once released, including not consuming alcohol or illicit drugs, obeying directions of a parole officer and not committing any jailable offences.
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