Work and Income double-killer Russell John Tully has lodged an appeal against his conviction and sentence of life imprisonment with a minimum non-parole period of 27 years.

Tully was found guilty in March of being the masked gunman who stormed the Ashburton Winz centre on September 1, 2014 and shot dead receptionist Peggy Noble, 67, from point blank range and three times shot case manager Susan Leigh Cleveland, 55, as she pleaded for her life.

The 50-year-old was also found guilty of attempting to murder case manager Kim Adams.

He was found not guilty of attempting to murder case manager Lindy Curtis who was shot in the leg and badly injured hiding under a desk.

In May, Justice Cameron Mander sentenced Tully to life imprisonment with a minimum non-parole period of 27 years - the second highest non-parole period ever handed down in New Zealand history.

Today, a Court of Appeal spokeswoman in Wellington confirmed that Tully has formally lodged an appeal against his conviction and sentence.

No date for any hearing has yet been set.

Throughout the court process, Tully always indicated he would always appeal whatever the outcome was.

At sentencing, he alleged a "major cover-up by the Crown" regarding disclosure and evidence, and further claimed he didn't have access to a lawyer.

Tully sacked at least six defence counsel.

"If I was guilty and went out and killed two people, I'd take it, and say, 'That was me'. But obviously that was not the case and I refute the accusation," Tully said.

Tully was found to be mentally capable of facing charges of double-murder and attempted murder after a hearing under the Criminal Procedure (Mentally Impaired Persons) Act 2003 in the High Court at Christchurch last year.

Justice Mander said he had no doubt that if staff hadn't fled the building, or if staff weren't fortunately absent that morning, there would likely have been more fatalities.

They were "cold-blooded executions", particularly callous and brutal, he said.

"This type of crime is rare in New Zealand," Justice Mander said.

Justice Mander said Tully was a "very dangerous person" who was very capable of extremely violent actions.