Police in 2012 released some documents from their inquiry under the Official Information Act, including witness statements.
However, Mr Banks' statement to police - given in a three-hour interview - was withheld, with Mr Banks refusing to agree to its release.
The Ombudsman's decision comes after a complaint from New Zealand Herald journalist David Fisher, who requested the release of the full transcript.
The Labour Party also laid a complaint with the Ombudsman.
Labour's associate security and intelligence spokesman Grant Robertson said if Mr Banks really had "nothing to fear, nothing to hide" he should have voluntarily allowed police to release his statement.
"John Banks must now be aware that his insistence on secrecy is a farce when there is already so much information about these allegations in the public arena," he said.
In an opinion, released today, Ombudsman Ron Paterson said the decision to withhold Mr Banks' statement in full was not justified, citing public interest grounds.
"I recommend that the police release a redacted statement to the requesters once the related court proceedings against Mr Banks have concluded."
Professor Paterson said the Official Information Act did not give good reason to withhold the statement at the time it was requested.
However, in light of the subsequent private prosecution, he delayed the statement's release because disclosure would likely prejudice Mr Banks' right to a fair trial.
Professor Paterson said public interest in the transparency and accountability of local electoral donations required access to the parts of Mr Banks' statement relating to the solicitation of campaign donations and contact with potential donors.
"Given the public disquiet about the integrity of the fundraising for the 2010 Auckland mayoral election, without direct access to Mr Banks' statement, the public will not be adequately informed."
Mr Banks is alleged to have knowingly received political donations from internet entrepreneur Kim Dotcom and SkyCity that were recorded as anonymous.
The allegations relate to two $25,000 donations from Dotcom and a $15,000 donation from SkyCity.
Police have previously released a redacted copy of the executive summary of their criminal assessment report, as well as letters to and from complainants, and statements from witnesses who had authorised their disclosure.
The documents shed light on the way Mr Banks' campaign team raised nearly $1 million during his 2010 Auckland mayoral bid, including drawing up a list of 10 rich donors who would be targeted for $25,000 each.
