A father who threw his toddler son "with everything I had" causing him to hit his head and die has pleaded guilty to torture and manslaughter.

Shane Purssell Akehurst was originally charged with murdering one-year-old Corby Mitchell Akehurst at Kin Kin in March 2015, but pleaded guilty to the lesser offence of manslaughter after it was downgraded in January.

He also pleaded guilty in the Supreme Court in Brisbane to torturing his son between November 13, 2014 and March 26, 2015.

The court heard Akehurst admitted throwing his son towards the bed — "probably with everything I had".

The toddler then hit his head on the timber wall and started convulsing, the court was told.

Crown prosecutor Mark Green said Akehust made a triple-0 call on March 25, 2015, alerting authorities that the 21-month-old was unresponsive.

The court heard the toddler was rushed to the intensive care unit, where staff noticed significant injuries on his small body.

He was declared brain dead and his life support was turned off two days later.

The court heard an autopsy confirmed Corby died after losing consciousness and going into cardiac arrest.

Supporters wearing "Justice for Corby" shirts outside the Supreme Court. ( ABC News: Mark Slade )

'Persistent, torturous conduct'

Mr Green said an MRI identified significant head trauma to the toddler, whose body, the court heard, was covered in 81 injuries, including multiple bruises, abrasions and fractures.

He explained not all of those injuries "were consistent with an intention to commit violence", but could not say how many.

Mr Green also said it was likely that in the days before he was taken to hospital Corby had been unwell due to infection.

He said Akehurst "intentionally inflicted pain and suffering" on his son over a four-month period, including "popping" Corby's ribs.

The prosecutor said Corby's death was the "inevitable consequence" of Akehurst's "persistent, torturous conduct" and he should be sentenced to at least 12 years' prison.

After initially denying causing the injuries, Akehurst later told police he had been home alone with Corby, who was "restless" and refusing to go to sleep.

"He continued to get angry with the child's behaviour and was continuously picking the child up and taking him back to the room," Mr Green said.

"He told police … he'd grabbed the child angrily with force — and it's been described in defence submissions as probably with "everything I had" — and threw the child back towards the bed.

"The child at that time hit his head on the wall behind his bed and started convulsing.

"[The] defendant indicated he was intending to throw the child on the bed and intended to hurt him.

"When asked whether he thought throwing the child would cause him harm, he indicated that he did not care at that point because he was so angry."

Mr Green said Akehurst admitted he knew there was "potential for something to go wrong".

He also described punching his son in the nose on March 22, 2015 "for not settling down at night", resulting in a black eye, as well as punching him again in the face the following night.

Father 'never bonded' with son

Defence barrister Rob East said his client was once a hardworking family man but due to long stints away as a FIFO worker, felt he "never bonded" with Corby.

"How could that possibly explain [what he did]?" Justice Martin Burns said.

Mr East said Akehurst was "hopeless" at getting Corby to settle, which irritated his wife, as well as himself.

He said the family was under financial strain and as time went on Akehurst developed anger issues — which he took out on his young son.

"The family was destroyed the day he took his son's life," he said.

"He instructs not a day goes by that he doesn't think about his son and what he did to him."