The man admitted to slicing the nose of his ex-wife with his thumb nail during an argument but said it was in self-defence.
The court heard how the pair's seven-year relationship was fraught with arguments.
The officer said he was always defending himself from his wife's attacks.
"She was always flying and attacking at me," he told the jury.
He said he couldn't "function at work" and struggled with mental health.
An ACC injury form filled out by the officer was produced as evidence. On it he wrote "restraining my wife from a violent episode. Already has been referred to police".
"He relies on the fact he was acting in self defence and preventing himself from suffering injury to face and eyes," defence lawyer Mark Ryan said during the trial.
"He has consistently denied being the aggressor ... in a volatile relationship," said Ryan.
The Crown alleged the officer was psychologically and physically abusive to his former stepson over a prolonged period of time, and was abusive towards his ex-wife during their marriage.
Allegations were first made by his ex-wife in 2009 and then raised again in 2017.
Ryan said it was a "tit for tat" situation that erupted when the couple were having custodial issues relating to their son.
A police report published in 2009 following an investigation into family violence allegations made against the officer concluded that no charges should be laid due to "insufficient evidence".
The officer was suspended from working for the New Zealand Police during the trial and has not yet returned.