John Christopher Walmsley, 36, was in July found guilty by an ACT Supreme Court jury of aiding and abetting the suicide of his girlfriend.

The troubled 25-year-old woman died after taking a lethal cocktail of heroin and prescription drugs on New Year's Day, 2011.

During the trial, jurors heard the woman met Walmsley at a rehabilitation centre in 2010 and began using heroin soon after.

The court heard Walmsley was present when the woman, who suffered bipolar disorder, wrote a will and suicide note.

He bought and prepared the drugs for their use in his Ainslie Village unit.

Walmsley woke about 3.25am to find foam and blood coming from the deceased's mouth.

He called triple-0 and performed CPR until emergency services arrived.

The Crown argued that Walmsley had acted to facilitate and encourage her death.

But Walmsley fought the charges, claiming neither of them was meant to die.

Justice John Burns, in handing down the sentence on Wednesday, said he was satisfied the pair had entered a suicide pact.

But the woman succeeded, and Walmsley survived.

The judge said he also accepted that Walmsley's thoughts were disturbed at the time but his moral culpability was still significant.

Justice Burns jailed Walmsley for four years, backdated to take into account time spent in custody, with a non-parole period of two years and four months.

He will be eligible for release in June 2015.