The jury at the High Court in Wellington reached the verdicts against Esarona David Lologa after less than three days of deliberations, rejecting the defence of insanity argued by Lologa's lawyers.
Lologa, 50, had been granted name suppression throughout the five-week trial, but the order was lifted when he was convicted.
Prosecutors accepted Lologa had schizophrenia when he twice set fires inside the 92-bed Loafers Lodge hostel in Wellington over one night in May 2023.
They said he lit the fatal blaze not because of his mental illness but because he wanted to seek a transfer to other accommodation.
Lologa's lawyers didn't deny their client lit the fires, but they said he was not guilty by reason of insanity. In New Zealand, this meant the jury must accept the defendant was incapable of understanding that his actions were wrong.
His lawyers said there was no evidence that he'd set the fires because he wanted to live elsewhere, but prosecutors said Lologa told people he didn't like living at the boarding house and wanted to move elsewhere.
Lologa first set a couch in a communal area ablaze late one evening, prompting an evacuation of the building. After residents put out the fire, he returned and placed cushions and a blanket in a cupboard before setting them alight.
He left the building without raising the alarm or calling emergency services.
During the trial, the court heard recordings of desperate phone calls to the fire department from people trapped inside and accounts from tenants, including one man who jumped from a window to escape the blaze.
In a police interview played for the jury, the man denied setting the fires, despite officers telling him he had been seen on security camera footage doing so, RNZ reported.
Some of the boarding house residents included social services clients and older, disabled and otherwise vulnerable people, as well as nurses working at a nearby hospital.
The burnt out building remains standing in the suburb of Newtown.
The residents who died included colourful and well-known Wellington identities. Michael Wahrlich was a veteran busker who juggled tennis balls and Liam Hockings' daily foot tours of the area made him a familiar face to locals. The other three victims were Kenneth Barnard, Peter O'Sullivan and Melvin Parun.
Murder carries a mandatory life sentence in New Zealand, with judges required to set a prison term of at least 10 years before an offender can apply for parole. Arson carries a sentence of up to 14 years in prison.
Lologa will be sentenced in November.