An Indigenous leader who stole almost $1m from Aboriginal organisations has been thrown behind bars for more than six years.

Three separate juries convicted Geoff Clark, 72, on 25 charges of theft, obtaining financial advantage by deception, perjury and knowingly dealing with the proceeds of crime.

The former chair of the disbanded Aboriginal and Torres Strait Islander Commission was found to have stolen $922,214 from four Indigenous organisations between 2001 and 2015.

Clark used $404,344 to pay legal fees as he faced criminal and civil proceedings in the early 2000s over historical cases of gang rape and an assault, a court heard.

He was ultimately convicted of obstructing police during an incident at Warrnambool’s Criterion Hotel, while a civil jury found he led two pack rapes against a teenage girl in the 1970s.

A further $56,020 went to housing expenses, including rates and electricity and water bills, a court heard.

County court judge Michael O’Connell on Friday described the offending as “carefully calculated” as he sentenced Clark to six years and two months behind bars.

Clark will be eligible for parole after serving three years and nine months.

“You contrived to conflate your own personal interests with the interests of the community,” O’Connell said.

“You betrayed its trust.”

Clark, who watched the hearing via video link from prison, looked down at his hands as the sentence was delivered.

His son, Jeremy, 51, was also sentenced on Friday to two years and two months in prison after he was found guilty of theft and false accounting.

However, his jail term was wholly suspended.

A jury determined Jeremy Clark had stolen $231,969 from the Aboriginal organisations to help fund his father’s legal fees.

He also pleaded guilty to wrongly obtaining $10,780 as a grant from the federal government.

Jeremy Clark was given a recognisance release order for his plea, requiring him to be of good behaviour for two years.