Hamilton, 62, is a former partner of DAC Legal and advised Belgrave Finance until its 2008 receivership.
The trial, which began in March, was jointly prosecuted by the Serious Fraud Office and Financial Markets Authority.
An SFO forensic accountant said Belgrave made around $12million of loans to entities effectively controlled by property developer Raymond Schofield.
Those loans breached Belgrave's debenture trust deed, the rules dictating the terms and conditions between investors and the company accepting the funds.
For the theft charges Hamilton was found guilty of, he was accused of helping Schofield and two other Belgrave directors with those loans and was therefore a party to their offending of theft by a person in a special relationship.
For those charges to stack up, the Crown had to prove Hamilton helped with the breaches, was aware of the offending and intended to assist with it.
The Crown's main allegation for those charges was that Hamilton assisted by receiving a portion of the loans in question into DAC Legal's Trust account. Justice Faire said Hamilton assisted with the offending by carrying out instructions to execute related-party loans.
The judge also said Hamilton had knowledge of the offending: "The surrounding circumstances make it entirely implausible that Mr Hamilton was not aware of the offending. On the evidence there is no doubt that, at the very least, Mr Hamilton was wilfully blind to the relevant elements of the offending," he said.
"Having found that Mr Hamilton had the relevant knowledge of the offending, I am satisfied beyond reasonable doubt that he intended to assist in the offending ... in light of his knowledge Mr Hamilton knew that his legal assistance was resulting in related-party lending," the judge said.
"Whatever his motive, Mr Hamilton was aware of what the legal documents and trust account were being used for, and intentionally facilitated the crime by providing such legal assistance."
Hamilton was also alleged to have formed a common intention with the other parties to prosecute a plan whereby funds would be sought from investors to make loans to the property developer and entities associated with him.
However, Justice Faire said he was not satisfied beyond reasonable doubt that Hamilton was involved in that manner.
Hamilton served as mayor of Central Hawke's Bay for six years.
He was Waipukurau Rotary Club president, Central Rugby and Sports Club chairman and was made a Member of the New Zealand Order of Merit in the 1997 Queen's Birthday Honours.
In May last year the New Zealand Lawyers and Conveyancers Disciplinary Tribunal ordered him struck off the roll of barristers and solicitors. It followed the Law Society bringing charges of misconduct against Hamilton.
He has not held a legal practising certificate since 2011, the same year in which he was facing bankruptcy proceedings due to an unpaid debt for the purchase of a Wellington brothel.
