However, the amount of work involved means the auditor, WHK Taylors, will only select a random sample of 650 transactions to check, which will then be scrutinised by council chief executive Jim Harland.
The move comes after the Otago Daily Times earlier this year reported the council's 687 full-time-equivalent staff had together spent millions of dollars on 206 ratepayer-funded credit cards in the past three years.
A detailed list of transactions made by the council's top 36 managers and four personal assistants was released in July, showing they together spent $534,500 on mainly legitimate council expenses.
The spending included $100,500 on food, coffee, entertainment and drink - deemed appropriate by Mr Harland - and $7000 on meetings in central city cafes.
Details of the remaining 166 cards have not been made public, with the council declining to collate and release the information unless costs of $8278 were paid up front.
Instead, Mr Harland said at the time he would scrutinise the transactions "line by line" himself.
Contacted this week, Mr Harland confirmed a random audit of 650 transactions was expected to be completed in the next few weeks.
The transactions would be selected by WHK Taylors and presented to Mr Harland, who would check each one, and their supporting invoices, to ensure the purchases met the "necessary business expenditure" test, he said.
"They are going to pull out the information, but someone's got to make a judgement call on whether the expenditure is a necessary business expenditure.
"That's a judgement and as the only employee of the councillors, I don't believe I can delegate that.
"It'll take me probably a day, but I think it's important to do that," Mr Harland said.
A report on the findings would be made public when presented to the finance and strategy committee, probably in November, Mr Harland said.
"It will be as public as it can be."
The auditor had already prepared a draft report on the council's one-up system of checking purchases, also to be presented to the committee next month, which found the system was "sound", Mr Harland said.
No other issues of concern had yet been highlighted, but Mr Harland said he had noticed a decline in the use of purchase cards across all staff since the council's spending habits were detailed.
