The first man convicted under New South Wales' one-punch laws has been jailed for more than 10 years for fatally punching Raynor Manalad outside a party at Rooty Hill in Sydney's west.

A jury found Hugh Garth guilty of unlawful assault causing death in May this year and the prison sentence was back dated to August 2014.

Raynor Manalad sustained extensive bleeding on the brain after the attack. ( Facebook )

Mr Manalad died in Westmead Hospital the day after the party, sustaining extensive bleeding on the brain.

During sentencing Judge Antony Townsden said alcohol-fuelled violence was all too common.

"Over recent years, the incidence of such offences, particularly when associated with the excessive consumption of alcohol, have been all too frequent," he said.

"Such offences are cause for grave disquiet and the community is understandably angry and frustrated by their occurrence."

Outside court Mr Manalad's mother Teresita said she had no sympathy for Garth and his family,

"I don't feel anything for him and the family, I won't waste any breath, any part of my brain for them," she said.

She and her husband pleaded with young men going out to drink alcohol to be responsible.

"Be responsible, be good, be kind and be the best version of yourself, take responsibility for your actions," she said.

Family's 'devastating loss'

During the trial Ms Manalad spoke passionately about her 21-year-old son "Ray", saying he was a nurse who wanted to help people battling alcohol addiction.

Judge Townsden spoke of the impact on Mrs Manalad and her family.

"Mrs Manalad spoke of the family's devastating loss and showed enormous courage and strength when speaking of her son's life which was cut short by the actions of the offender," he told the court.

"I wish to extend my deepest sympathy to the family members in their loss and would also say every unlawful taking of a human life harms the community in some way."

In sentencing Judge Townsden told the court Garth had shown no remorse and did not take any responsibility for his actions.

He said his prospects for rehabilitation were not good.

The one-punch laws were introduced across the state in January 2014 to try to curb the number of deaths from single punch attacks.

The laws prescribed an eight-year minimum sentence for anyone who found guilty of fatally striking a person with a single punch while drunk or under the influence of drugs.

Garth admitted he had drunk a lot of alcohol on the night Mr Manalad died, but said he was acting in self-defence during the altercation outside the party.