But a judge has warned Jonathan Monaghan his conditional chance to avoid spending more time behind bars "ain't going to be easy".

Acting Justice Richard Refshauge sentenced the 31-year-old father in the ACT Supreme Court on Wednesday to four years in jail.

The term was backdated to reflect time already served, with the balance suspended in favour of a two-year drug and alcohol treatment order and associated good behaviour order.

Monaghan, who was described as having a "shocking" and "depressing" criminal record listing some 93 offences, was on parole at the time of his latest offending.

Early on Christmas Eve in 2019, he carried out what Acting Justice Refshauge said was an unplanned and "clearly opportunistic" armed robbery in Hawker.

Monaghan approached the victim's car as the man went to the boot to take out clothing he was about to put into a charity donation bin.

The serial criminal reached through one of the car's open windows and grabbed the victim's wallet, which contained $740 in cash, from the dashboard.

As he did so, he "jabbed" a "rusty-looking" knife in the man's direction and warned him: "Don't come to me."

Monaghan eventually chucked the wallet onto the ground and ran, having taken a sum of money from it.

Police subsequently issued a media release with CCTV images of Monaghan in the area, and received "several" Crime Stoppers reports identifying him.

He was not arrested, however, until January 6 last year, when he was busted behind the wheel of a grey Mazda that had been swiped from a Melba street.

The owner had parked the vehicle there, "full of treasured possessions and basic survival gear in preparation for an emergency bushfire evacuation".

Police tracked the sedan down at the Caltex service station in Watson within hours of it being reported stolen.

Officers repeatedly yelled at Monaghan to stop and surrender, but he defiantly rammed two police cars in an unsuccessful bid to avoid apprehension.

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The 31-year-old remained in custody from that day onwards until he appeared in court on Wednesday morning.

Prior to his sentencing, he pleaded guilty to charges of aggravated robbery, dishonestly driving a motor vehicle without consent, failing to stop for police, and driving without ever having held a licence.

Monaghan was also found guilty by Chief Magistrate Lorraine Walker of dangerous driving, having unsuccessfully argued his actions at the petrol station had merely been negligent.

In sentencing, Acting Justice Refshauge said the robbery "must've been terrifying" for the victim, noting that "a knife is always loaded".

He also said Monaghan had "no reason ... to be driving", let alone smashing into police cars in the later incident.

The judge noted that Monaghan had committed all of the relevant crimes before, with the exception of dangerous driving.

"I've seen you too many times in this court," Acting Justice Refshauge told the offender.

"What I've done in the past hasn't worked.

"Hopefully we've cracked it this time [with the drug and alcohol treatment order]."

The judge said he was satisfied Monaghan was suitable for such an order because the man repeatedly committed crimes to support "a strong and entrenched drug habit".

He ordered Monaghan to travel directly from court to Canberra Recovery Services in Fyshwick, where the 31-year-old must complete a residential rehabilitation program.

Acting Justice Refshauge warned Monaghan "it ain't going to be easy" to leave behind the lifestyle he had lived "for a long time".

But he said the court's drug and alcohol sentencing list program would provide ongoing support if Monaghan was willing "to come to the party".

"Good luck," Acting Justice Refshauge told the 31-year-old on his way out of the courtroom.

"No mucking up, alright?"

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