Walker met Mrs South in Wellington in the late 1990s when he acted for her in property deals.
They became friends and, upon the death of her husband, Walker gained her trust and was granted power of attorney over her affairs.
In November 2007, Mrs South sold her property in Wellington and made arrangements with Walker to purchase a property at Dick Street, Reefton for $70,000.
Walker's lawyer Doug Taffs told the court today that Walker had put forward $10,000 of his own money towards a deposit on the house, but a mortgage did not come through and he lost his money.
He then used Ms South's money to pay off debts.
He convinced a wealthy colleague to buy the property, who would later sell it to Mrs South when she had enough money to pay.
"Unfortunately Mr Walker did not explain that to Mrs South," Mr Taffs said.
Mrs South moved in, and paid for repairs to the house but eventually after three years learned she had no legal claim to the property because her $70,000 cheque had been banked into Walker's own account. By then Walker's dishonesty had left her penniless.
Walker had an "unjustified optimism"that he would be able to recoup and repay the money, Mr Taffs said.
In April 2011, the Real Estate Agents Authority struck Walker off and he was now bankrupt, he said.
Karen Grau for the Crown said it was an "extreme breach of trust of an elderly lady who treated him like a son".
"She ended up penniless in a property that she didn't own and it was the community who kept her going."
Mrs South's fortunes picked up in mid-2011 when the Professionals, the real estate agency Walker had been associated with, reimbursed her the $70,000 and the Mad Butcher franchise bought a house in Reefton for her to live in rent-free for the rest of her days.
However, her tenure was just five months. Mrs South died on December 19, 2011.
Judge Bruce Davidson said the offending would have been extremely stressful for Mrs South, who was in the later stages of her life "where she was entitled to a restful and peaceful life".
There was a strong suspicion that gambling was behind his offending, Judge Davidson said.
As well as the home detention, Walker was sentenced to 200 hours' community work and ordered to pay reparation of $7500 at $25 per week.
He was also to attend gambling counselling and surrender his firearms.
