Former Health Services Union boss Kathy Jackson defrauded members of more than $100,000.
The union's ex-national secretary on Monday pleaded guilty to two charges of obtaining financial advantage by deception.
Court documents show she misused her job to evade $67,792.85 in personal credit card debt between July 2003 and November 2010.
Her admissions lift a legal cone of silence from an earlier jury verdict which found Jackson guilty of two similar offences relating to about $35,000.
When Jackson took the stand in Victoria's County Court last year, she denied any wrongdoing.
"I absolutely did not take any money that I was not entitled to, I did not steal from the HSU," she told the jury.
"I am just absolutely devastated that I have ended up in this position by trying to do the right thing."
After a two-month trial, jurors found her guilty of twice obtaining financial advantage by deception, but cleared her of more than a dozen counts of theft and obtaining property by deception.
Jackson transferred $22,000 in union funds in 2008 to buy a Mercedes Benz from the husband of the union's former legal advisor.
She also claimed $13,100 for travel reimbursements from the union for travel and accommodation in the United States.
In the offences admitted on Monday, Jackson claimed money from the union for personal items including travel.
Jackson was the union's national secretary from 2008 to 2015, collecting a salary in excess of $100,000 to oversee the movement that represents health professionals including doctors, nurses and paramedics.
She was lauded for blowing the whistle on her predecessor, former Labor MP Craig Thomson, and former union general secretary Michael Williamson in 2011.
Williamson was later jailed for leeching almost $1 million from the union and recruiting others to hinder a police investigation.
Thomson was fined $25,000 following his conviction for 13 counts of theft.
After Jackson's own fall from grace, she declared bankruptcy.
The Federal Court ruled she owed the union $2.4 million, including for funds misappropriated for groceries, travel, entertainment and even her divorce.
Jackson will return to court for sentencing at a later date.