Sydney one-punch accused refused bail

The first person charged under NSW's new one-punch laws will remain behind bars after an unsuccessful bail bid in the Supreme Court.

Hugh Garth is accused of fatally punching Sydney nursing graduate Raynor Tristan Castillo Manalad, 21, outside a house party in Minchinbury, in Sydney's west, in May.

Garth was the first person to be charged with assault causing death while intoxicated and faces a minimum eight years jail if convicted.

In court today, Garth promised to abstain from drinking, undergo random breath tests, adhere to a curfew and leave his family's home in Blacktown only under his mother's supervision.

"In essence (you're) prepared to put yourself under house arrest," barrister Scott Schaudin put to his client, who appeared via video link.

Mr Schaudin said a statement from a sober guest at the Minchinbury party suggested Garth wasn't the first person to use his hands in the incident.

But Acting Justice Anthony Blackmore refused bail, saying the proposed restrictions did not go far enough in ensuring Garth would not abscond.

"(It's) a very serious offence. It carries a mandatory minimum sentence of eight years in prison," he said.

"The crown case appears to be strong ... given the nature of the penalty here, there must be at least a risk of non-appearance."

Garth's mother and girlfriend were in court to support him.

The NSW government passed new laws this year aimed at tackling drunken violence in response to a spate of high-profile assaults.