Locke pleaded guilty on the day the trial was due to start after the charge was reduced from wounding with reckless disregard to injuring with reckless disregard. He is currently serving a 16-month jail term.
The MP said a new, stand-alone offence was required to send a message about the seriousness of that kind of assault. He knew of past cases in which juries had been reluctant to convict an offender of manslaughter, even though death had resulted.
A new charge would offer an alternative to juries, and to defence lawyers who wanted to plea-bargain to avoid a trial.
The new charge, which would carry a maximum sentence of 20 years, placing it between wounding with intent to cause grievous bodily harm (14 years) and manslaughter (life), was designed to cover any fatal unprovoked attack made without warning.
Unlike a similar law passed in Australia after a series of fatal assaults there, it was not limited to punches to the head or neck.
He was planning to ask NZ First for support but it could be next year before the bill was debated. If it became law he wanted to see it accompanied by a publicity campaign highlighting the dangers of one-punch assaults and the potential 20-year penalty.
Other bills drawn in Thursday's ballot covered high-powered laser pointers, shark cage diving and second-language learning in schools.