The Australian white supremacist who murdered 51 Muslim worshippers at two mosques in Christchurch in 2019 has been prevented from appealing against his guilty pleas, after one of New Zealand’s highest courts said his bid was “utterly devoid of merit”.

Brenton Tarrant, who is responsible for the worst mass shooting in New Zealand’s history, asked the court of appeal in February to allow him to appeal against his guilty pleas, claiming harsh prison conditions had affected his mental health and compelled him to admit to the crimes.

In a decision released on Thursday, the court said it did not accept Tarrant’s evidence about his mental state, which was inconsistent with detailed observations of prison authorities, mental health professionals and trial lawyers.

“He endeavoured to mislead us about his state of mind in a weak attempt to advance an appeal in circumstances where all other evidence demonstrated that he made an informed and totally rational decision to plead guilty.”

The court said Tarrant was not coerced or pressured in any way to plead guilty.

“The evidence overwhelmingly demonstrates that he was not suffering any significant psychological impacts as a result of his prison conditions at the time he pleaded guilty.”

Tarrant also failed to adequately explain the delay in filing his notice of appeal, despite having access to lawyers, the court said.

“The court concludes that Mr Tarrant’s proposed appeal is utterly devoid of merit.”

Tarrant pleaded guilty in March 2020 to 51 counts of murder, 40 counts of attempted murder and a terrorism charge, after initially saying he would defend the charges. In August 2020, Tarrant became the first person in New Zealand to be sentenced to life in prison without the chance of ever walking free.

But in 2022 he filed an appeal at the court of appeal, for both his convictions and his sentence. The court had to first consider whether the appeal could proceed because it was filed outside the legislated time frame to do so.

During the week-long hearing, which began on 9 February, Tarrant told the panel of three judges his mental health had deteriorated due to conditions in prison, where he was held in solitary confinement, with limited reading material or contact with other prisoners.

He said he was suffering “nervous exhaustion” by the time he entered his guilty pleas, and he had admitted to the crimes just months before his trial was due to begin because he felt there was “little else I could do”.

Tarrant, a self-declared white supremacist, said he had masked his mental illness, partly driven by the “political movement I’m a part of” and said he had made a late application because he had not had access to the information required to make it.

Tarrant’s former lawyers, psychologists and prison staff also gave evidence during the hearing, challenging Tarrant’s claims of mental health distress and harsh prison conditions. Experts had ruled Tarrant was fit to enter pleas.

The crown lawyer Barnaby Hawes told the court that Tarrant was “an unreliable witness and his narrative should be treated with caution”. Further, evidence of his guilt – including livestreaming the attacks – was so overwhelming, a guilty verdict would be assured if his case went back to trial, Hawes said.

Tarrant moved to New Zealand in 2017 planning to carry out a white supremacist attack. He planned the mass shooting for months, conducted reconnaissance at the mosques, distributed a manifesto expressing his racist views before he opened fire, and live-streamed part of the assault on Facebook.

After the attack, Jacinda Ardern’s government banned military-style semi-automatic rifles and created a firearms registry.

An inquiry into the attacks is the largest coronial investigation New Zealand has seen and is still under way. In October 2025 the high court left the door open for Tarrant to be called as a witness despite objections from survivors and families of the victims.