Mark Lundy will spend an extra three years in prison before being eligible for parole.
Lundy's appeal against his convictions for murdering his wife and their 7-year-old daughter two years ago was rejected by the Court of Appeal in Wellington this morning.
The court did not accept the defence case that the weight of the evidence went against a guilty verdict but did accept the Crown application to increase Lundy's non-parole jail term to 20 years.
Lundy's sentence is the longest non-parole period of imprisonment for a life sentence ever handed down in New Zealand.
Previously the longest fixed term sentence imposed was on Taffy Hotene, who killed Auckland journalist Kylie Jones and received an 18-year non-parole sentence.
Other offenders, including serial rapists Joseph Thompson and Malcolm Rewa, were sentenced to longer non-parole periods of at least 25 years and 22 years respectively when they were sentenced to preventive detention.
Lundy was found guilty in March of the brutal axe killings of 38-year-old Christine and daughter Amber in their Palmerston North home in August 2000.
During a dramatic seven-week trial Lundy took the witness stand and vehemently denied he was the killer.
He was sentenced to life imprisonment with a minimum non-parole period of 17 years.
Mike Behrens, QC, representing Lundy, has said the appeal was based on the verdicts being unreasonable and not supported by the evidence.
Lundy was not in court to hear the decision.
Court of Appeal Justices Tipping, McGrath and Glazebrook said in their decision today that a 15-year non-parole period would have been appropriate if the charge against Lundy was one of killing his wife alone.
"The question becomes whether an additional two years was a sufficient recognition of the need for very strong denunciation of the killing of Amber as well as that of Mrs Lundy."
The judges said Amber must have died with the awful injuries to her mother as her last living memory.
"We have to say that Mr Lundy's murder of his daughter in these circumstances, coming on top of the murder of his wife, requires denunciation and demonstration of society's abhorrence at a very high level.
"The trial judge did not, in our view, give this aspect of the case enough weight. He really only mentioned the involvement of Amber in passing."
They said Lundy's actions were "the grossest imaginable of violence". He had massively breached trust by attacking people who trusted him in their own home.
Law experts earlier this year said the Crown was entitled to ask for minimum mandatory non-parole periods greater than the statutory minimum.
Scott Opticon, senior lecturer in criminal procedure at the University of Auckland's Faculty of Law said the fact Lundy killed both his wife and daughter and possibly intended to collect life insurance were "aggravating factors".
He said the gruesome and heinous nature of the Lundy murders was the main issue in sentencing.
University of Otago Associate Professor of Law Geoff Hall said the Lundy case had parallels to the Bain family killings and the New Plymouth murder of police witness Christopher Crean.
"I would put it in the category of killing a witness (Amber)."
The other significant factor was the degree of planning that appeared to have gone into the murders.
- HERALD STAFF and NZPA