"Your reputation both publicly and privately is in tatters and this is a significant fall from grace," said Judge David Robinson.
The court heard Whelan had paid back all the stolen cash, covered the costs of his father's funeral and met his siblings to apologise for his actions.
Nevertheless, the judge said, there was a "sense of betrayal" and the victims spoke of how the ordeal had hampered their ability to grieve.
In June 2015, James Robert Whelan's health was in decline and he gave his son power of attorney over his property, an act that set in train more than five years of fraud.
A police summary showed the defendant regularly withdrew "large sums of cash" from ATMs at the Dunedin Casino, which sometimes totalled more than $1000 in a day.
By August 2019, Whelan had racked up gambling costs of $101,040.
Another $40,000 was withdrawn from other terminals around Dunedin, the court heard.
When the repeated deceit was finally uncovered, Whelan had siphoned off $147,709 — about half what was in his father's account.
The defendant was not long retired following a lengthy period working in "high-pressure prominent roles" when the fraud began.
He told Probation in a pre-sentence interview that he had missed the thrill his employment gave him, and turned to gambling which "provided an adrenaline rush and a sense of fulfilment".
The court heard Whelan had since sought help from the Problem Gambling Foundation and not placed a bet in a year.
He said he felt "toxic shame" and a loss of mana over his transgressions.
A search for Whelan online shows several photos of him involved in philanthropic pursuits over recent years.
One depicts him handling food donations bound for the Dunedin Night Shelter while another sees him beaming while receiving a cheque for $1000 on behalf of the Anglican Family Care food bank.
Counsel Anne Stevens QC said her client had a plethora of voluntary community involvement behind him, particularly in the Catholic Church, and stressed he had no criminal history.
Whelan had since resigned from his charity roles and now planned to be a role model to help other addicts, she said.
Stevens said the fact the defendant's father never discovered his son's betrayal helped the defence case, but Judge Robinson disagreed.
"It was his state that left him in ignorance, whether or not he was aware of the thefts carries no weight," he said. "The reality is his assets were targeted because of his inability to understand what was going on."
As well as the home detention, Whelan was sentenced to 180 hours' community work.
Getting help
If you, or someone you know, needs help with a gambling problem, the Gambling Helpline is available seven days a week at 0800 654 655 or by text 8006.
Other specialist contacts are:
• Māori gambling helpline - 0800 654 656
• Vai Lelei Pasifika gambling helpline - 0800 654 657
• Youth gambling helpline "In Ya Face" - 0800 654 659
• Gambling debt helpline - 0800 654 658
Or go to gamblinghelpline.co.nz.
