Mr Smillie failed to calm down, then the officer struck him with a baton and pushed him against a fence in an effort to apply handcuffs. Mr Smillie fell to the ground.
The officer then retrieved his Taser and warned Mr Smillie he would be Tasered if he continued to refuse arrest. Taser Cam footage showed the officer then released the Taser for 13 seconds before attempting to handcuff Mr Smillie. He then picked up the Taser and discharged it a second time.
"The authority finds that the deployment of the Taser on two occasions amounted to an excessive use of force and was contrary to the law," Sir David said.
"This was aggravated by the fact that on the first occasion the Taser was used for an extended period of time of 13 seconds.
"The first use of the Taser was not in self-defence, as claimed by the officer and given there were other options open to the officer short of using the Taser, the authority considers Mr Smillie's arrest could have been effected less forcefully after waiting for the arrival of other police officers."
Bay of Plenty police said they conducted a criminal investigation and sought legal advice over the officer's actions.
"We fully accept that the actions of the officer when using the Taser didn't meet the high standards we expect," said Bay of Plenty District Commander Superintendent Glenn Dunbier.
"However we are satisfied his actions were not the result of any ill will or malicious intent.
"Our staff confront incredibly difficult and emotive situations on a daily basis and are making split second judgements and decisions without issue.
"We accept that the officer's judgement on occasion was flawed.
"He has learnt from that situation and responded well to remedial action."
Mr Dunbier said that action consisted of one-to-one training with a focus on judgement when using tactical options, particularly the Taser.
Since the incident the officer had passed the yearly Taser certification testing three times, he said.
He said the IPCA recommendation of disciplinary action had been noted.
"However the public rightly expects police to deal with these issues in a timely manner and we initiated remedial action through the employment process some time ago.
"Anyone involved in employment matters will understand that in good faith we cannot take different action now."
Ms Ardern said either the Government needed to ensure the IPCA completed cases in a more timely manner, or there needed to be acknowledgement by the police that employment matters would be revisited when a report such as this was released.