In an email sent to NZ First membership last week Mr Peters appealed for them to put the events of 2008 behind them and prepare for the 2011 election campaign.
"Before we make a new beginning we want to use the hardest word in the English language -- SORRY," Mr Peters is reported to have said.
"We acknowledge that we made mistakes. In keeping our eyes on the big picture, we failed to appreciate the importance of the details."
The party is holding its annual meeting on August 29 where Mr Peters' leadership will be discussed.
Before last election the party was mired in controversy over election spending and an always tense relationship between Mr Peters and the media became acrimonious.
Mr Brown has welcomed the apology and said Mr Peters was to blame for the party failing to return to Parliament.
"I have to be absolutely upfront, I don't think the team made terribly many mistakes at all," Mr Brown told Radio New Zealand.
"We stuck to the script and we put all our efforts in so the reason we didn't clear the 5 percent in particular rests totally on Winston's shoulders."
Mr Brown said Mr Peters' antagonistic approach had not done the party any favours and he thought his judgement clouded.
"He attacked the media far too often, and he attacked the National Party to the degree that John Key announced he wouldn't deal with us."
Mr Brown criticised a web campaign and open letter attacking National and media.
"All hell broke loose," Mr Brown said.
The letter prompted intense reaction from the public and some staff left phones off the hook.
The apology would go some way towards rebuilding bridges.
"I am quite happy to be part of the "we" are sorry. I want Winston to stay as leader, he has got all the attributes all the abilities that we need and he's got them in abundance."
However, he said Mr Peters' style had to change.
"It's a team thing that will get New Zealand First back in Parliament if we are to do it and Winston's got to understand as leader he's got to be part of the team and stop playing from time to time the lone ranger of politics."
Mr Brown thought some party members would give Mr Peters another chance.
"I think they will agree with me there's got to be some accountability there, he can't just go do whatever he wants whenever he wants and we've got to be more media friendly, we've got to answer the questions, we've got to take a leaf out of John Key's book. John Key is always pleasant, he always answers the questions, and he comes always from a considered position.
"And that's what Winston could do and should do."
Despite his criticism Mr Brown remained loyal and said Mr Peters was "a bloody nice guy".
Mr Peters spent most of 2008 defending revelations that his party had channelled large donations through secret trusts to avoid disclosure.
This culminated in controversy over a $100,000 donation from expat businessman Owen Glenn towards Mr Peters' legal fees.
At the time Mr Peters was foreign minister and he pushed for Mr Glenn to be appointed honorary consul in Monaco.
At first Mr Peters denied the donation happened and once it became public denied that he knew about it.
A parliamentary inquiry found on the balance of evidence Mr Peters had known about the donation and he was censured for not disclosing it.
Various authorities investigated Mr Peters but no charges were laid.
Mr Peters recently appeared on TVNZ's Q&A programme to attack the Government's consideration of repealing the foreshore and seabed legislation.
