A Darwin man has been sentenced to six years in prison with a non-parole period of three years for a brutal head stomp assault on a stranger outside a pub on Darwin's nightclub strip.

Key points: Vulnerable man who was no threat attacked, judge says

Vulnerable man who was no threat attacked, judge says CCTV shows Namaibai punching and stomping on victim

CCTV shows Namaibai punching and stomping on victim Namaibai's claims of remorse rejected by judge

Yowane Raymond Namaibai, 23, pleaded guilty in the Northern Territory Supreme Court to unlawfully causing serious harm.

The violent attack happened on Mitchell Street on August 16 last year and left victim Nicholas Gray with a fractured skull and brain bleed.

"He [Namaibai] and his co-offenders aggressively attacked a vulnerable man who was no threat whatsoever," sentencing judge Justice Judith Kelly said.

In handing down the sentence, Justice Kelly told the court Mr Gray was drunk and trying to get a taxi when Namaibai "deliberately followed him across the road and confronted him".

"It was a vicious, sudden and relatively prolonged attack by the three of you on the victim," Justice Kelly said.

Media prohibited from publishing CCTV of assault

Extensive security footage of the incident showed Namaibai and his friends Jack West and Roberto Spice approach Mr Gray before a minor altercation, which then led to Namaibai punching the man to the ground.

Namaibai then proceeded to kick and stomp on Mr Gray while he tried to cover his face with his arms.

Security staff and bystanders intervened at that point but Namaibai pushed past them to deliver one final stomp on Mr Gray's head, which rendered him unconscious on the footpath.

Justice Kelly prohibited the media from publishing images of the incident online.

Mr Gray underwent surgery and spent six days in hospital.

'Embarrassed, ashamed, mortified: Namaibai apology

In an apology letter written by Namaibai from jail and presented to Justice Kelly in court through his defence lawyer Shane McMaster, Namaibai said he was "embarrassed, ashamed, [and] mortified by what he did".

But Justice Kelly responded: "I do not believe that Namaibai is remorseful… Actions speak louder than words."

Justice Kelly said Namaibai's description of the incident was "completely at odds with the incident that we witnessed in the CCTV footage".

The court heard Namaibai initially denied he was involved in the attack and refused to participate in an interview with police.

He had a long history of violent offending with prior convictions in the Northern Territory, Queensland and South Australia, Justice Kelly said.

"He has a deplorable record of breaking court orders," Justice Kelly said.

At the time of the Mitchell Street attack, Namaibai was four months into a suspended sentence for another violent incident.

His co-offenders West and Spice were also arrested over the incident and also pleaded guilty.