Tane Tahi Manawa, 38, died about 45 minutes later.
Marius was sentenced to life behind bars for the murder on Friday after a jury found him guilty the previous day.
The aspiring rapper also admitted robbing a pizza delivery man of food at knifepoint and injecting an 18-year-old with meth, delaying calling an ambulance and then lying to paramedics.
In extraordinarily awful consequences the woman became a paraplegic, Brisbane Supreme Court Justice Glenn Martin said.
When the now 30-year-old picked up the metal bar from the garage in Mr Manawa's Surfers Paradise house in May 2019, he had the intent to at least cause him grievous bodily harm, the court found.
"The assault upon the sleeping Mr Manawa was cowardly, it was brutal, it was unflinching," Justice Martin said.
"It was demonstrative of a callous disregard and could not on any view of any of the circumstances have been generated by anything that had been done to you."
The two-week trial heard evidence of Marius being poorly treated by Mr Manawa but Justice Martin did not regard that as having any particular influence.
"It seems that the catalyst for what you did was your view of his treatment of you, together with the fact that you were very hungry," he told Marius.
The hunger may have been from coming down after not having had methamphetamine for about five days, but he had also not eaten for a considerable time.
Mr Manawa was speaking glowingly about the lunch he had just eaten.
The father-of-two was a talented artist with a quirky sense of humour who loved food and was passionate about helping others to find themselves, his mother Jacqui Kaui told the court.
"To you, the one now found guilty of the murder of my son ... I tell you to your face, I forgive you," she told Marius.
"There has been enough pain and anguish, heartache for you too."
Marius pleaded guilty on Friday to grievous bodily harm for injecting the 18-year-old with meth and the armed robbery of the delivery driver.
While the woman asked Marius to give her the drug, he delayed calling emergency services before lying to paramedics saying the unconscious teen had had a seizure.
Justice Martin ordered Marius be eligible to apply for parole only after serving 21 years behind bars instead of the usual two decades.
"It is appropriate to acknowledge the seriousness of this offence together with the other two very serious offences in this way," he added.
Marius has been in custody since May 2019.
