Mr Wairau did not agree with the details outlined in the police summary of facts relating to the Saturday night incident and wanted to be able to challenge it in court. He intended to continue his by-election campaign as well, which concluded on June 29.
Electoral Commission said only the death or incapacity of a candidate would affect the delivery of a by-election.
"A sitting MP will lose their seat if they are convicted of an offence that is punishable by imprisonment for a term of two years or more."
Mr Wairau, 37, said he had been involved in gangs when he lived in the Bay and had been "in and out of jail" when he was 16 to 27 years of age. He said his jail time had not been more than two years.
He moved to Palmerston North to "get away from it all" and to change his life.
"I've got a past. I've done a lot of bad things and I guess you could say some people from that past caught up with me (on Saturday night).
"I've tried to step away from all of that to better myself, change my way of thinking. I've been able to do that since moving to Palmerston North. I would like to give something back, maybe work as a community worker with youth."
Mr Wairau contested the Ikaroa-Rawhiti seat at the 2011 general election and put his name forward again for the by-election because he did not think any of the main parties represented "my view on life".
"I still care about issues such as home ownership, employment. Hawke's Bay has got seasonal work but it's only for four months of the year and then there's nothing afterwards.
"We need to do something about getting more jobs for our people."