So heinous were his crimes against 9-year-old Bradyn.

Instead, Justice John Burns sentenced the Canberra man on Monday to 36 years in jail for the boy's murder, and a total of 41 years for the whole of the beatings doled out to the boy and others.

Dillon's conduct towards his son, the judge said, could "aptly be described as torture".

"The truth is that the particular acts which caused Bradyn’s death were not isolated or out of character," Justice Burns said.

"Those acts were simply the culmination of a brutal process of torture of Bradyn that you engaged in over many months."

Dillon, 40, pleaded guilty in the ACT Supreme Court last year to murdering Bradyn.

The court heard how Dillon used his fists, lit cigarettes and belts to beat the boy repeatedly for months.

Dillon bashed the boy's head at least twice in the space of two months, causing bruising and bleeding to his brain. A final assault in February 2016 knocked the boy out and caused his old injuries to bleed again.

On that day, February 15, Dillon told the boy to bend over a marble coffee table while he beat him with a belt.

He kicked Bradyn in the abdomen, and then landed another flurry of blows, before the boy fell unconscious.

He never woke up.

The court heard it was the aggregated brain injuries that caused Bradyn's death.

Dillon never called for help, instead spending the afternoon while his son lay unconcious visiting the supermarket and selling an Xbox 360 to a neighbour.

He Googled "what does it mean if someone is knock out how do you get them up".

When police and paramedics eventually arrived, they found blood-spatter stains across the house.

Bradyn was unconscious, not breathing, and had no pulse.

His body was covered in more than 80 separate bruises, lacerations, as well as cigarette burns from where Dillon had put a lit cigarette out on the boy's skin.

He had broken bones, chipped teeth and scars.

In scathing sentencing remarks delivered in the ACT Supreme Court on Monday, Justice John Burns said the only reason the Dillon did not receive a life sentence was his plea of guilty.

He said the community benefits from a guilty plea, and if that was not recognised with a reduction in sentence, there would be less incentive for guilty offenders to plead guilty.

The man's beatings of the 9-year-old boy were brutal, cowardly and callous, the judge said.

He referred more than once to Dillon's "torture" of his son.

And Justice Burns said the man had behaved "despicably", lying about the boy's behaviour and attempting to minimise his responsibilty.

As the judge delivered his sentence for the murder, Bradyn's mother Rachel Jones and Bradyn's family and friends erupted with sounds of relief, and cried out the word "yes".

Dillon, in a grey prison tracksuit, did not react.

He was handcuffed and led away by corrections officers.

Speaking outside court, Ms Jones said there was no comprehending the abuse Dillon inflicted on Bradyn.

"No sentence that could have been handed down today against this vicious and cowardly predator could ever give me satisfaction," she told the waiting media.

"We have lost our little boy in the most callous and brutal ways, nothing will give Bradyn his life back or bring him home to me and his siblings."

Ms Jones said a lot of people had failed Bradyn, who she remembered as a loving, caring boy, who "gave his everything to make sure everyone else was happy around him".

Dillon was also sentenced on Monday for violent assaults on a woman between 2011 and 2013, including throwing a knife into her knee, attacking her with a hammer and threatening to slit her throat.

The judge set a non-parole term of 32 years.

Dillon will be eligible for parole in February 2048, when he is 69.