Matthew Gagalowicz, 37, was convicted of manslaughter in NSW in 2005 and sentenced to 10 years' jail on appeal with a six-year non-parole period, his criminal history states.

He fronted the ACT Magistrates Court on Wednesday after pleading guilty to nearly a dozen charges, including assault, damage property and unlawful possession of stolen property.

Gagalowicz, also known as Matthew McPetrie, had fought one count of assault occasioning bodily harm but was found guilty after a hearing.

The court heard for that charge, he headbutted his victim, whom he blamed for his lost wallet, in the face causing the victim's nose to be split open.

Court documents state that in April 2021, Gagalowicz, wearing a balaclava and beanie and pushing a trolley, went to McDonald's in Dickson where he tried to open a food cabinet.

The duty manager confronted him and said words to the effect of: "mate, what you're doing is very wrong, I need you to leave the store right now".

Gagalowicz then rammed his trolley into one of the self-serve kiosks before yelling at a staff member.

The offender then headbutted the glass window of the store, causing a spider crack.

Police later found him and noticed "a small reddish lump" in the middle of his forehead.

About one year prior, Gagalowicz was on the ground yelling at people near Dickson Woolworths when a man and his mother walked past.

The woman told Gagalowicz to shut up before he and the other man started shouting at each other.

The offender then headbutted him, causing his nose to bleed immediately.

Other offences include Gagalowicz stealing $1128 worth of clothes from a Canberra Centre store and about $100 of items from a 7-Eleven in January this year.

In May, he stole a $499 barcode scanner from a city store and hundreds of dollars worth of alcohol from a Braddon liquor store.

In his sentencing remarks, magistrate James Stewart said the assaults were "quite vicious" and the property damage at McDonald's "is pretty remarkable".

"My concern is that this man's going to keep on headbutting people and he's wreaked some real damage," Mr Stewart said.

"He's ultra violent and ultra dangerous."

Mr Stewart said the headbutt causing a broken nose was "a brutal act of violence" and reading the facts "concerns me deeply".

"This man's ultra intelligent and ultra talented. It's disturbing he's coming back before the court with his early violence history," he said.

Mr Stewart sentenced Gagalowicz to a 12-month partially suspended jail term backdated to May 27 to account for his pre-sentence custody.

The magistrate said "out of all the people that's come before this court, boy oh boy you've got some talent".

"I'd give a kidney to have 1/10th of your musical talent ... You need to get your life back on track," Mr Stewart said.

MORE COURT AND CRIME NEWS

Earlier in the sentencing, defence lawyer Eddie Chen said after his client was released for manslaughter, he did "very well initially and things happened in his life that caused his wheels to fall off".

"On this occasion ... he's taken a lot of steps to try to find out the way forward," Mr Chen said.

In his argument for leniency, Mr Chen said Gagalowicz had compiled plans to take as part of his rehabilitation.

"[He] Should be given this chance to try to correct the trajectory of his life," he said.

However, senior prosecutor Claire Daly said Gagalowicz's rehabilitation plans have not shown "evidence of any attempts at rehabilitation".

She described his offending as "extreme examples of personal violence" having "the hallmarks of random unprovoked attacks towards unassuming people".

Ms Daly said the prosecution had strong cases for most of the charges and that Gagalowicz, who has spent about one-third of his life so far in custody, had not shown remorse.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: