Walsh's alleged co-attacker, Jacob Patrick Broderick, 17, however pleaded not guilty to the same charge as the pair stood in the dock together.
The teenagers had been drinking at Turks Bar in Havelock North earlier during the night, as had the victim's group. However, they were not known to each other.
When the bar closed at 3am the victim and his friends made their way to McDonald's on Havelock Rd, while Walsh and Broderick walked about the village allegedly attempting to initiate a fight with another group of men, court documents said.
At about 3.50am Walsh approached the victim by the public toilets trying to "antagonise and wind him up" while pestering him for a cigarette, before one of the teens allegedly said: "I should just smack him over."
After the victim's friends entered the toilets the electrician was attacked "without warning or provocation" and Walsh began punching him on the head up to seven times until his knuckles bled.
"At one point Walsh believed the victim was dazed and semi-conscious from the force of his blows but he continued to strike the victim to the head," court documents stated.
"Near the end of the attack Walsh also kicked the victim in the jaw using the base of his foot ... Walsh could tell from the amount of blood from the victim's nose that he had had enough."
Immediately following the assault Walsh and Broderick then made their way to McDonald's where Walsh bragged openly about how he had beaten the 32-year-old with his bare hands.
The victim's family told Hawke's Bay Today yesterday their brother's vision and speech had since returned, after he spent five days in Hawke's Bay Hospital and 24 hours in an induced coma.
"He hasn't gone back to work yet ... he has a lot of issues he's dealing with," the victim's sister said.
She had said it was "terrifying" to find her "gentle" brother lying unrecognisable in a hospital bed after the assault.
Her sibling has suffered from several ongoing issues including headaches, fatigue, balance and co-ordination issues and neck and upper chest pain.
Walsh was convicted and remanded on bail until October 22, when Judge Tony Adeane asked for Walsh to go through the restorative justice process. While Broderick was remanded on bail until a case review hearing on November 10.
The teens went to St John's College together before Broderick attended Hastings Boys' High School and established himself as an accomplished sports player at age group level in Hawke's Bay while also playing club cricket for Cornwall Cricket Club in Hastings.
The maximum penalty for injuring with intent to cause grievous bodily harm is 10 years in prison.