Anthony Catanzariti, 24, was on trial for six charges relating to a "long night" of violence against a man who owed him $2500 in drug money in July 2012.

But on Wednesday, the third day of proceedings, the ACT Supreme Court was informed that the trial had taken a sudden and unexpected turn.

Catanzariti pleaded guilty to sexual intercourse without consent and two acts of indecency, and the Crown indicated it would withdraw the other charges.

That ended the trial before the evidence of the first witness was completed.

Catanzariti is already in prison for other, unrelated offences.

Last week, he was sentenced by Justice John Burns to two years and four months imprisonment for bashing a jewellery-wearing friend who he accused of thinking he was "so bling".

He took more than $14,000 in gold jewellery from the man.

The sentence was backdated to July 2012, and Catanzariti would have been eligible for parole in February on the unrelated charges.

But he will now face sentencing for the current offences, which took place after Catanzariti went to an apartment where the victim was having beers with friends one night in July 2012.

He walked in with his girlfriend and another man, making the victim and his friends uncomfortable.

Catanzariti soon began slapping, punching, and elbowing the man.

During what the Crown described as a "long night", Catanzariti sexually assaulted the man with a beer bottle and made a dog commit indecent acts on him, among other things.

The victim was able to leave the home the next day, and went to police to report the attack.

He was taken to hospital, where 27 individual injuries were found.

Catanzariti was arrested, and his trial began before Justice Hilary Penfold in the ACT Supreme Court on Monday.

The plea deal means prosecutors are expected to withdraw three charges.

Sentencing will begin on June 19.