The Employment Relations Authority said Hart served seven years in prison for the crime.
Hart had worked for seven weeks at Auckland's Printlounge before its general manager, Stephen Sheppard, became aware of his criminal history.
During Hart's job interview in early January this year, he said he had recently served two years in prison for assaulting a man at a party.
Mr Sheppard told the authority he had asked if Hart had other convictions, but Hart denied this.
Hart was offered the job because Mr Sheppard wanted to give Hart a second chance, the authority said.
"Unknown to Mr Sheppard at the time of making the job offer, Hart had a more extensive criminal record," it said.
In February, Mr Sheppard received a call from someone alerting him to Hart's murder conviction.
Mr Sheppard confronted Hart about the information, who admitted the conviction and was immediately fired, the authority said.
Authority member Robin Arthur said it was likely Mr Sheppard did ask if Hart had any other convictions.
"His difficult employment prospects were a strong motivation to say 'no' to Mr Sheppard's question and I considered that was more likely than not what had happened." Mr Sheppard was left with the impression that Hart's assault conviction was a "one-off", Mr Arthur said.
After the conviction was discovered, Mr Sheppard told the authority he fired Hart because other staff might become fearful and leave, he could lose customers, and there was a loss of trust and confidence in Hart.
Mr Arthur said Mr Sheppard called Hart to a meeting without any notice or the right to bring a representative.
In this case, Hart was "entirely responsible" for the situation because he gave incomplete information to Mr Sheppard, Mr Arthur said.
He awarded no compensation, but said Hart should have been paid a week's notice, which could be resolved during a costs agreement.
additional reporting Anna Leask of the New Zealand Herald
