The Corrections Department confirmed "a high-profile prisoner" was found dead in his cell last night.
His death has been referred to the coroner.
The announcement of his death came as his lawyer Barry Hart and the Crown were due at the High Court at Auckland to make preparations for his sentencing, after a retrial last year.
A prison source told NZPA Dixon had suffered head and neck injuries and died in his cell.
Dixon was one of the country's most high profile criminals, having been convicted for a 2003 rampage which included attacking two women near Thames with a samurai sword, severing or partly severing their hands.
During the same P-fuelled rampage he drove to Auckland and killed James Te Aute by shooting him repeatedly in the back.
He was convicted two years later on charges including murder and kidnapping, receiving a 20-year minimum sentence, but that was appealed on insanity grounds and a re-trial granted.
At that five-week retrial in June last year Dixon was again convicted on several charges including murder and was in custody awaiting sentence.
Details about his upbringing emerged during his trials, including alleged sexual abuse on him as a child and incidents of him being kept outside tethered to a clothesline.
His defence argued he was insane, but the Crown countered that he was "not mad, but bad".
Lawyer Mr Hart said in December last year he planned to appeal the second conviction and try to get a third trial.
He was vague about the grounds he planned to base the case on.
Dixon has managed to maintain a profile while in prison.
He was recently understood to have tried to pull a makeshift weapon on Mr Hart during a prison visit.
In December 2007 he used a fork to try to gouge out the eye of a fellow prisoner, who required hospitalisation.
It was later discovered Dixon had his own MySpace web page with comments about his crimes and photos of him in prison on it.
