A Geelong man has been sentenced to eight years' jail for killing a 22-year-old man with a single punch after leaving a popular bar in Melbourne's CBD.

Richard Vincec, from the suburb of Herne Hill, had pleaded guilty to the manslaughter of Jaiden Walker after leaving Cherry Bar in May.

The father of three, whose youngest child is still a baby, can apply for parole in five years.

Jaiden Walker died in hospital several days after being punched. ( Supplied )

Supreme Court Justice Peter Riordan accepted Vincec did not go out looking for a fight and was deeply remorseful.

But he said his unreasonable and unnecessary actions had taken the life of "a fine young man".

"Your decision to punch the deceased was made on the spur of the moment," he said.

"Your culpability is aggravated by the fact that after your violent act, you responded not by stopping to help your victim, but by fleeing the scene."

The court had previously heard Vincec had been "let off the leash" by his partner that night and had got drunk and high on cocaine and speed.

Both men visited several venues with different people before ending up at Cherry Bar in AC/DC Lane.

Later, Vincec, 26, was seen on CCTV kissing a woman, with whom Mr Walker had previously been in a relationship, outside the Chanel clothing store on Russell St.

The situation between Mr Walker and Vincec became "hostile", the court heard, and Vincec tried unsuccessfully to shake Mr Walker's hand, telling him, "Shake my hand, I'm not a dog".

Mr Walker eventually agreed but squeezed his hand in the process, to which Vincec responded, "Grab my hand like that and I'll hit you".

Mr Walker responded, "I'll do what I want, mate."

Seconds later, Vincec struck Mr Walker in the left cheek, causing him to fall back and hit his head on the ground, the court was told.

Richard Vincec wrote an apology letter to the Walker family after Jaiden's death. ( AAP: Mal Fairclough, file photo )

One of Vincec's friends tried unsuccessfully to intervene before the fatal blow.

Mr Walker died in hospital several days later, after suffering a fractured skull and bleeding on the brain.

Family and remorse factored into sentence

His father, Jon Walker, welcomed the eight-year term.

"It was probably where I thought the sentencing would go, so it's unfortunate his family has now lost their dad for a period of time, a long period of time," Mr Walker said.

"One person made a really bad decision that's ruined two families, impacted so many others.

"In a split second there's so many things that can change."

Vincec, who has previous convictions for violent offending, wrote an apology letter to the Walker family.

Jon Walker said two families had been ruined by one bad decision. ( AAP: Mal Fairclough, file )

In setting the prison term, Justice Riordan took into account Vincec's "very good prospects for rehabilitation", supportive partner, three young children, stable employment and previous compliance with bail conditions.

He said the punishment needed to take into account the widespread community concern about one-punch attacks.

"As a result of your actions, a fine young man has been deprived of the rest of his adult life," Justice Riordan said.

"You appear to be truly remorseful and your prospects of rehabilitation are very good."

Vincec wiped away tears and took deep breaths throughout the sentencing, taking a final look at supporters before being escorted from the court.