Joshua Alessandro Nabytowicz-Cannizzaro, 22, got behind the wheel in May 2020 so badly affected by alcohol and methamphetamine that a medical expert later found he would have been incapable of properly controlling a car.

The P-plater drove from Harrison to McKellar and was on his way back to suburban Gungahlin, via Kaleen, when he swerved to avoid "something furry" and lost control of his silver Ford Falcon.

Nabytowicz-Cannizzaro hit a guard rail on Baldwin Drive and rolled the car, leaving himself with ailments including a broken sternum.

But as chief magistrate Lorraine Walker said in the ACT Magistrates Court on Thursday, the consequences for a boy in the back seat were far more grave.

The youngster had, the previous day, told the court of feeling like "the main character from my horror movie" when he woke up after spending weeks in a coma.

His lower right leg was damaged to the point it was "unsalvageable" and had to be amputated just below the knee, while a fat embolism caused by his broken femur resulted in a traumatic brain injury.

These were just a few of the many significant afflictions the teenage boy suffered.

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Indeed, Ms Walker said, it would be difficult to overstate the impact of the crash on the victim and his family, which had been torn apart as his parents separated.

The victim's mother was now his full-time carer, she said, while the boy's father had lost employment because of his constant efforts to make himself available to help.

Ms Walker said Nabytowicz-Cannizzaro was clearly sorry for all of the destruction wrought by his impulsive and poor decision to drive while under the influence.

She noted he had been forthcoming with investigating police, and he had pleaded guilty to a charge of culpable driving causing grievous bodily harm at an early stage of the court process.

The chief magistrate added the 22-year-old had instructed his lawyers not to challenge any aspect of the prosecution case during his sentence hearing, and he had sought a referral for restorative justice.

"I am persuaded that his remorse is deep and genuine," Ms Walker said.

The sentencing exercise was a challenging one for the chief magistrate, who observed that an intensive correction order might benefit Nabytowicz-Cannizzaro's rehabilitation and protect the community by helping him not to reoffend.

But, in the end, she was not satisfied such a sentence would recognise the harm done to the victim or adequately deter other drivers from similar offending.

Ms Walker therefore sentenced Nabytowicz-Cannizzaro to two years in jail, ordering that the balance of the term be suspended once he has served six months in custody.

The 22-year-old, who was also disqualified from driving for 12 months, will be subject to a three-year good behaviour order upon his release from prison.

"I accept that you're sorry for what you've done, and I'm sure you understand the great harm that you caused," Ms Walker told the offender.

"There's a penalty to be paid for that harm, and that's a penalty you're about to commence today."

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