Former Health Services Union boss Michael Williamson has been jailed for at least five years for systematically defrauding the union of almost $1 million and hindering a police investigation.

Williamson showed no emotion as he was sentenced to a maximum seven-and-a-half years at Sydney’s District Court on Friday.

In a damning judgement, Judge David Frearson said Williamson oversaw a “parasitic plundering of the union funds for pure greed”.

The frauds were calculated, brazen and arrogant and involved an “extreme” breach of trust.

“(It was) a reprehensible betrayal of the union and all its members,” he said.

It comes almost 20 years after Williamson became general secretary of the union.

During his tenure he presided over an increase in salaries significantly above industry levels.

It was obvious, Judge Frearson said, Williamson exercised “some kind of supreme power”.

“He encouraged loyalty and regarded those who supported him.”

From around the time his offending started, Williamson was “handsomely paid indeed”, earning more than $500,000 by 2011, the judge said.

At the same time, Williamson began “systematically” defrauding the union representing healthcare workers.

In one instance – carried out from 2006 to 2009 – the former boss created numerous false invoices made out to the company CANME, which was in his wife’s name.

More than $340,000 was paid for work never done.

Once inquiries began, the father of five then tried to cover up his offending and recruited others to hinder a subsequent police investigation.

Judge Frearson said Williamson had developed a “reprehensible sense of entitlement”.

But he said he was remorseful, had taken full responsibility for his actions and had apologised to union members for his actions.

He also accepted he was of prior good character and that there was little chance he would reoffend.

The former ALP national president’s earliest date of release is March 2019.

Outside court, a small band of union members have gathered with placards that read, “Major crime needs tough sentence” and “No excuse for stealing and lying”.

Whistleblower Kathy Jackson said questions still needed to be answered.

“Michael Williamson’s power was not challenged in that organisation. My concern is that those people are still there, people who weren’t prepared to stand up,” she told reporters outside court.

“We still have an organisation that is riddled with power corruption and hopefully the royal commission will deal with that.”

Commander of fraud and cyber crime squad Detective Superintendent Arthur Katsogiannis said the sentence was “reassuring”.

“The decision also ensures that those people wanting to report corruption in the workplace can feel confident in coming forward and doing so,” he told reporters.