Justice Patrick Keane said Dawson had been drinking and left Spy Bar before colliding with a group of people.
He made a racist remark to one of Murray's friends before he was knocked to the ground and slapped about the face.
A doorman intervened and Mr Dawson was allowed to get to his feet and walk away.
But as he left he continued to yell and that's when Murray approached him.
Eyewitnesses described Murray's punch as a "forceful" blow which knocked Dawson out before he hit the ground. One described hearing a "sickening thud" as Mr Dawson's head hit the pavement.
While Mr Dawson lay unconscious on the ground with blood coming from his face, Murray got into a taxi with his mates and headed to another bar.
Mr Dawson died the following day in hospital.
Justice Keane said the jury did not agree with Murray's suggestion of self-defence.
He said evidence at trial suggested Mr Dawson had a broken bone in his face.
"This evidence convinces me that when you punched Mr Dawson, you must have intended to do so with as much force as you could have mustered," Justice Keane said.
Ms Kennedy told Murray that "Billy was ruined for no reason" and her last memories of her friend are seeing him in hospital before he died.
"You took my friend and left a big gap in his place and I feel angry all the time."
A statement was read from Mr Dawson's mother Lee. She said the Christchurch family had not attended court for Murray's trial or sentencing because they wanted to focus on Mr Dawson's life - not his death.
Mr Dawson's brother-in-law Coen Lammers also had his statement read and said the death had devastated his family.
"Not only has he beaten Billy to death, he has also beaten the stuffing out of all of us."
He said Mr Dawson was killed on his wife's birthday so her special day will "never be the same again".
"I hope the defendant will have plenty of moments to consider how much he has affected the lives of our family and countless others."
Speaking from Takaka this afternoon, Mr Lammers told APNZ he had taken the family on holiday. He said he felt the sentence was a little on the low side but it makes no difference.
"It's not going to bring him back".
Mr Lammers said he hates the word "closure" because there is no such thing: "It's just nice that the whole thing is finished."