A suspended Queensland policeman who killed his baby son with a "sickening" single punch has been jailed for nine years.

Brisbane's Supreme Court heard Colin David Randall "forcefully punched the defenceless 10-week-old" so hard it caused fatal abdominal injuries, in an attack at the family home at Victoria Point on Brisbane's bayside in 2014.

Justice Peter Davis said in sentencing it was "obvious that once you had delivered the blow to the defenceless baby's abdomen, his death was inevitable".

"His liver was shattered, other organs had been severely damaged and his aorta ruptured," Justice Davis told the court.

"Once you had delivered the blow, no medical treatment could save him."

The fatal blow was delivered the first day Randall had been left alone with his son, while his wife and four-year-old daughter went to the shops.

Justice Davis said Randall instinctively lied after it happened — firstly to his wife, then ambulance officers and ultimately investigating police.

"You then pretended that the injuries which were later found were caused accidentally by you and perhaps others when applying CPR," Justice Davis told the court.

"This, of course, was complete nonsense."

As a former police officer, Randall will serve his sentence in solitary confinement. He will not be eligible for parole until 2021.

The court heard the defendant was frustrated at the time due to a lack of sleep from working night-shifts, co-sleeping with children and his wife being sick with the flu.

A failed attempt to transfer from Wynnum to Hervey Bay station also factored in Randall's frustration.

The court heard he wanted to move to be near a female officer he had an affair with.

'A willed act of violence to a defenceless infant': Judge

The 41-year-old had maintained his son had suffered some unexplained health issue and that his injuries were caused by the application of CPR.

Justice Davis said Randall persisted with that "ridiculous" story until a week before his murder trial, when he decided to plead to the lesser charge of manslaughter.

"He was a 10-week-old baby and totally innocent of the world," Justice Davis told the court.

"He had no idea of the duty you had to care for him."

The court heard that while the Crown accepted the blow was "utterly spontaneous", that did not mean there was no intent.

"It was a punch … it was a willed act of violence to a defenceless infant," Justice Davis said.

"A punch is an act which is intended to hurt."

The baby was in a swing when the punch was delivered.

Randall remained without emotion during the hour-long sentencing hearing.

Justice Davis did not accept that Randall was remorseful and said his decision to enter a late guilty plea to manslaughter was a matter of "self-preservation".

The charges came after a year-long joint investigation by the Queensland Police State Crime Command, child protection unit, Ethical Standards Command and the Crime and Corruption Commission.

The officer was suspended on full pay a month after his son's death.

The Queensland Police Service suspended Randall without pay when he was charged and will now go through the formal process of discharging him.