Christopher John Miles, 35, was due to stand trial in June over two armed robberies at southside betting venues.

Instead he pleaded guilty to charges of aggravated robbery on the morning he was due to face an ACT Supreme Court jury.

Miles also asked the court to take into account another aggravated robbery charge and one count of car theft when he appeared at a sentencing hearing before Acting Justice John Nield on Thursday.

Miles and another man - armed with a knife and a pinch bar - stormed the Erindale Vikings Club about 3.45am in July 2009.

They tied up staff with cable ties before breaking into the club's poker machines, causing $90,000 in damage in the process.

The pair fled with $748 when another cleaner arrived for work.

A gun-wielding Miles and his co-offender also raided the Erindale ACTTAB about 9.40pm on Cox Plate day in 2010, the betting agency's second biggest day of the year.

The robbers forced a security guard and customers against a wall before getting an employee to open the safe. They got away with more than $46,000.

During the third robbery, a Wanniassa newsagency employee was confronted and bound by the two men about 5.05am in August 2009.

They took cigarettes, magazines and cash before escaping in the staff member's car.

Miles, from the witness box on Thursday, said he pleaded guilty partly to avoid his son being forced to give evidence against him.

The court heard Miles, who had previous convictions for armed robbery, was a heroin addict who went back to hold-ups to support his habit.

''I was broke and desperate,'' Miles said.

Miles was read a moving victim impact statement during a previous hearing. Asked what effect he thought the robbery had on his victim's life, he cried and said: ''Wrecked it.''

Defence barrister Shane Gill said the gun was incapable of firing and there was no violence in any of the three heists. But the Crown said the victims did not know that.

''The whole point was to terrify them, and terrify them into handing the money over,'' prosecutor Margaret Jones said. The impact on the victims had been profound, including one suffering post-traumatic stress disorder, she said.

Justice Nield will hand down judgment in October.