TVNZ's chief executive Kevin Kenrick says in hindsight it was a mistake to take Shane Taurima back on after Taurima's first attempt to enter politics for Labour, but said Mr Taurima had assured them he had no further political ambitions.
Mr Taurima resigned yesterday after confirming to his bosses that he hoped to seek Labour's candidacy for the Tamaki Makaurau electorate.
Leaked documents given to 3 News showed he had taken part in a Labour Party Tamaki Makaurau electorate meeting on how to win the Maori vote and that TVNZ staff had hosted a Labour Party meeting in TVNZ's offices last August, although Mr Taurima has denied knowing about the meeting.
In a statement, Mr Kenrick announced TVNZ would call in an external expert to investigate the work of the Maori and Pacific unit Mr Taurima led over the last year to ensure its editorial independence had not been impacted on.
It will also investigate the use by some staff of TVNZ resources, such as its offices and email system, for party political activities.
Mr Kenrick said people were asking why Mr Taurima was taken back on after seeking Ikaroa-Rawhiti, which went to Meka Whaitiri instead.
"The answer is, at the time we sought and received assurances from Shane that he had no further political ambitions. When asked to choose between journalism and politics, he chose journalism. With the benefit of hindsight that decision was a mistake."
The review would be led by Brent McAnulty, TVNZ's Head of Legal and Corporate Affairs, and would report to Mr Kenrick. The findings of both reviews would be made public once completed. Mr Kenrick said the review team would have access to all TVNZ's internal records.
"This investigation will be conducted as a matter of priority but it won't be a rush job we're focussed on carrying out a robust and comprehensive investigation that looks into this matter thoroughly.
"Given our position as New Zealand's most watched news provider we hold ourselves to the highest standards of editorial independence and balance. Clearly a line has been crossed here it's unacceptable and we make no excuses for what's happened."
He said the focus was on finding out what had happened and ensuring it did not happen again.