Reginald Stockwell diverted cancer charity donations into his own bank account to pay off debts, go overseas and impress his wife.
Stockwell stole $456,430 from a Victorian chapter of the Royal Antediluvian Order of Buffaloes between 2012 and 2019.
He used his job as the Grand Lodge of Victoria's financial controller to siphon off charity donations.
This included money meant for Melbourne's Peter MacCallum Cancer Centre, the Olivia Newton John Foundation, Make-A-Wish Foundation and Diabetes Australia.
Stockwell instead used the funds for personal expenses including a car, paying off credit card debts and visiting his Indonesian wife.
Some of the money also went to a horse trainer and gambling.
At one point he gave another Grand Lodge member a cheque meant for charity so that man could also pay off his debts.
Stockwell, 63, pleaded guilty in Victoria's County Court on Tuesday to 13 charges of theft from the fraternity at Geelong.
His lawyer, Timothy Sullivan, said Stockwell stole the money to keep up the perception of a wealthier lifestyle.
"It seems he's gone over to Indonesia and presented himself as having more money than he does," Mr Sullivan told the court.
"He's trying to put it on also to his wife that he's in a more stable financial situation than he is."
Stockwell worked for the Commonwealth Bank for nearly 20 years before leaving in the 1990s and getting involved in horse racing.
His finances then began deteriorating.
At one point, Stockwell used $50,000 of the fraternity's money to buy himself a car.
But he rationalised it because he needed to drive around Victoria for the Grand Lodge, and also gave other members a lift.
Stockwell was the fraternity's grand secretary for 18 years before being fired last year.
The Grand Lodge told the court its membership with the Royal Antediluvian Order of Buffaloes was in doubt because of Stockwell's misdeeds.
"You have stolen so much and managed to manipulate the narrative so that others are to blame," Robert Mackay said in a statement on the organisation's behalf.
Stockwell acknowledged he faced jail time.
He was remanded in custody to be sentenced on November 18.
Australian Associated Press