Helen Mary Rosamond, 48, falsified and inflated invoices from her event management company Human Group, swindling more than $19 million from the National Australia Bank between 2013 and 2018.
A jury found Rosamond guilty in November, finding she gave corrupt benefits to Rosemary Rogers, former chief-of-staff to NAB chief executives, and obtained or attempted to obtain property by deception.
"The overarching motivation of the offender is accurately described as one of greed, self-gratification and enrichment," Judge Robert Sutherland said on Thursday, sentencing Rosamond to 15 years in prison with a non-parole period of eight years.
Successfully hiding her derived financial benefit from her own company and even her co-offender, Rosamond defrauded the bank for almost five years, a testament to her level of planning, the judge said.
Rogers pleaded guilty to corruptly receiving benefits for her role in the same scheme in February 2020 and is serving a maximum jail sentence of eight years with a non-parole period of four years and four months.
The judge rejected submissions seeking to place greater blame on Rosamond's co-offender.
Rather than being dominated by Rogers, Rosamond and her co-offender clearly depended on each other to conduct the fraud, for which they were equally culpable, the judge said.
"During the years in which the fraud continued, both Rosemary Rogers inside the bank, and Helen Rosamond within Human Group, were extremely efficient," the judge said.
Rogers received a house, a BMW, boat, holidays and other benefits, Rosamond's trial heard.
Human Group began conducting legitimate work for NAB in 2006, before starting to defraud it in 2013.
Rogers would ensure contracts were extended with Human Group and pay its inflated invoices, with a delegated authority to approve spending up to $20 million.
When a new CEO took over, they did not know Rogers had such authority.
The judge said such a large authorisation exemplified the level of influence and trust Rogers enjoyed within the bank, which she abused.
Rosamond had not breached the trust placed in her at the same level, but also engaged in repeated and ongoing deception of her own company.
Her claim she wanted to express remorse, which came through "an apparently unquestioning third-party", was treated with "considerable reserve" by the judge, as Rosamond herself gave no evidence.
She will be eligible for release in December 2030.
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