At a Wellington Court of Appeal hearing in February, Wirihana's lawyer, Russell Fairbrother QC, said his client's involvement in the drug ring was low-level.
He said Wirihana was a "small-time user", who used meth to get through long working days while he worked two jobs.
Fairbrother argued Wirihana's sentence should be adjusted because of a change in the standard the courts used to judge similar offences.
The justice system had recently adopted a new standard for this type of offending - different to the previous standard Wirihana had been sentenced in line with - and his sentence should now be "scaled back accordingly", he said.
In a judgement released today, the judges granted the appeal and quashed Wirihana's original sentence, substituting it with one of home detention.
They said the circumstances of the case were "quite unusual".
"Mr Wirihana was a contributing member of the community. He had a full-time job, and he and his partner had a cleaning business franchise," the judgement said.
"It appeared he used methamphetamine to remain awake so he could work two jobs. He was not an addict."
Wirihana stored 336g of meth at his home on a co-offender's behalf, but made no money for doing so.
He also sourced a small amount of meth to supply to other people.
Sentencing Wirihana was difficult because the sentencing judge was bound by case law, which indicated sentences based on the quantity of drugs involved.
But new case law meant the sentence could now focus on Wirihana's lesser involvement in the offending.
As directed by the sentencing judge, Wirihana has been on bail since his sentencing, so has not yet served any of his prison sentence.
An updated report on his circumstances show that during this time he has kept his full-time job, maintained his relationship with his partner, and completed drug and alcohol counselling.
He is subject to random drug testing at his job and gave evidence of his clear results.
"It is almost three years since his offending. We understand he has spent the whole of that period on bail. His conduct during that time evidences not only prospects of, but actual, rehabilitation.
"He has taken steps to address the causes of his offending and he is willing to take more. He has a stable and supportive family life and is a valued and contributing member of society. He is drug-free. The likelihood of him reoffending is assessed as low."
Sending him to prison now would have a "disproportionately severe effect" and would destroy the benefits of the progress Wirihana had made.
The judges allowed larger discounts to Wirihana's end sentence for his personal circumstances, which allowed the prison term to drop down to a level which could be swapped for home detention.
