Justice John Burns sentenced Troy Michael Kennewell, 20, to three years and one month in prison, setting a non-parole term of 18 months.

The judge told Kennewell that it was "vital that you cease carrying weapons and in particular knives".

Kennewell had been charged with three counts of recklessly causing grievous bodily harm after stabbing a man who intervened in a fight between him and his girlfriend.

But the ACT Supreme Court also heard that after he was released on bail to live in NSW he was jailed for another stabbing incident.

When he was released from the NSW jail midway through last year he was immediately arrested and extradited to the ACT to face the ACT charges.

While in custody at the Alexander Maconochie Centre he was caught carrying a shiv.

On the ACT charges, Justice John Burns rejected Kennewell's suggestion that he had been provoked.

He said the stabbing, three discrete motions which all produced serious injury, was brief but vicious.

The court was told that during the incident on October 21, 2017, Kennewell had been at a house party in Kambah when he and his girlfriend began arguing over alleged infidelity.

The argument caught the attention of a passer-by, who looked over a fence and saw a man pushing a woman in the chest.

He approached the couple, and Kennewell said "she f--kin' cheated on me".

The passer-by replied "So what?"

Kennewell then stabbed the man in his wrist, shoulder and abdomen before fleeing the scene, leaving behind a bag containing his wallet and identification.

The victim would likely suffer long-term injury, including scarring and pain, the court was told.