It found the officer could not have arrested Roulston without using the Taser.
Roulston had been drinking bourbon whiskey with his cousin in the evening of the incident, despite advice from his doctor not to consume alcohol while on medication for a head injury he had sustained a few years earlier.
A fight broke out between the two men, and Roulston was described as being violent and confused.
He was accused of running to a neighbouring house and smashing a bedroom window, badly cutting his arm.
One of the occupants of the neighbouring home confronted Roulston and hit him with a rake.
Callers to 111 told police there was a street fight, there had been a woman screaming and one man was armed with a "pole".
The two officers sent to the scene were named as Officer A and Officer B by the IPCA.
Officer A was trained in using a Taser and was granted permission from his supervisor to use the Taser if necessary.
At the home, Roulston swore at the police and threw a brick at them, which bounced and hit Officer A in the shin.
He threw a second brick at the officers before Officer A drew his Taser. He told Roulston four times to get down on the ground but he did not comply.
"After his efforts to communicate with Mr Roulston had failed, Officer A discharged his Taser once," the IPCA said.
"Mr Roulston fell backwards, hitting his head on the driveway."
The authority said the officer "believed on reasonable grounds that Mr Roulston was assaultive, posed a real threat of physical injury and could not be arrested using less force".
It also found the officers provided the appropriate medical care once Roulston had been Tasered.
Roulston later pleaded guilty to assault with a weapon and wilful damage, and was sentenced to 300 hours community work.
Canterbury District Commander Superintendent Gary Knowles said the officer's actions "were entirely appropriate and justified" and the independent investigation painted "a very different picture of the events ... from what was portrayed in some news media" last year.
"We are disappointed at the selective coverage of the incident by some media, which provided a narrow view of what occurred based on a few seconds of video footage at the end of the incident," Mr Knowles said.
"The IPCA findings have however vindicated our actions in this case, despite selective reporting to the contrary."
Tasers have been presented 1532 times and discharged 212 times between when they were introduced to New Zealand police in March 2010 and June last year.
"Every decision to use a Taser is taken with careful consideration and only where other options are considered unlikely to be effective," Mr Knowles said.
"Officers are faced with making split-second decisions based on the circumstances they are faced with, and virtually without exception they get it right."
