The Independent Commission Against Corruption (ICAC) heard today Mr Macdonald was paid $450,000 and stood to benefit much more as a pay-off for approving a lucrative coal mining lease for Mr Obeid's family.
Counsel assisting the inquiry Geoffrey Watson produced banking records for an account controlled by Mr Macdonald, showing that from September 1, 2010, until last July, there were monthly deposits of $25,000, eventually scaled back to $15,000, which totalled $450,000.
The money was coming from one of Mr Macdonald's mates, John Gerathy, a businessman and lawyer who was involved in coal mining deals.
The money stopped flowing six days after ICAC put Mr Gerathy on notice that they wanted the records of his financial dealings with Mr Macdonald.
In a curious act, Mr Gerathy then put a sudden caveat over Mr Macdonald's property for the same figure, $450,000.
The inquiry's lawyers believe he was reverse-engineering an alibi to paper over the true purpose of the payments.
They believe the $450,000 is a down payment to an eventual payday of larger payments, which have only failed to occur because ICAC's enquiries have stymied the scheme.
It is the first time the corruption inquiry has directly accused Mr Macdonald of receiving a financial benefit from the suspect deal.
The disgraced politician denies the allegation.
Geoffrey Watson: Mr Macdonald, the truth is you were going to get a cut out of your dealings with the Obeids, weren't you?
Ian Macdonald: No.
Watson: And you were going to get a cut out of dealings with (Greg) Jones.
Watson: And you were trying to get a bigger cut, because you wanted a cut out of the whole of the Cascade profits, didn't you?
Watson: And the only thing that frustrated that occurring, has been the intervention of ICAC, hasn't it?
Watson: Maybe not just ICAC. Also the press pressure building up, and preventing any overt payments being made to you.
Macdonald: No. I wasn't going to get anything out of any of those.
Earlier in the day, Mr Macdonald was asked why he had 14 bank accounts and said he could not recall why.
He also admitted receiving $30,000 from coal investor Greg Jones, but told the inquiry it was for wedding and birthday presents.
Mr Jones was also an investor in Cascade Coal, a company associated with the Obeid family in a project in the Bylong Valley in the Upper Hunter region of New South Wales.
ICAC also attempted to discredit other evidence from Mr Macdonald.
He was show an atlas that he previously told ICAC he had found a reference to a Mount Penny in and had used to decide where this mining tenement would be located.
Mr Macdonald said he found this reference in 15 seconds, but neither the Commissioner David Ipp nor Mr Watson could replicate that act.
Mr Watson rounded on Mr Macdonald, describing his story of a chance finding of Mount Penny in an atlas as "a load of hooey".
Undeterred, Mr Macdonald quipped: "I'm good at geography."
It was an inquiry about the Obeid-Macdonald political mateship, which drew an arch observation from Mr Macdonald that he preferred to speak to his friend on the phone, as his parliament house office was a right-wing cave he tried to avoid.
Mr Macdonald will be back for further questioning tomorrow, after which the hearing will go into a recess for a few weeks before opening a new chapter of enquiries about mining leases Mr Macdonald granted elsewhere in the Upper Hunter region.