A Queensland mother whose son took his own life just hours after learning he owed a Centrelink debt says she hopes the Royal Commission into the Robodebt Scheme will bring about justice and accountability for victims.

"We need to know who is responsible for this and people need to be held accountable," Kath Madgwick said before the first hearing of the royal commission got underway in Brisbane.

Her son, Jarrad Madgwick, was suffering mental health issues when he discovered he owed a debt of just under $2,000.

He was applying for Centrelink after losing his job when he received the debt.

"It was wrong, it should never have occurred, and a machine shouldn't be dealing with vulnerable people," Ms Madgwick said.

Robodebt is the name given to the automated debt recovery program from 2015 to 2019, which unlawfully claimed almost $2 billion from more than 400,000 people.

Commissioner Catherine Holmes called for those willing to share their experience of the Robodebt scheme to make a submission to reveal the "human impact" of what occurred.

"This was a difficult stressful time in the lives of thousands of people who were told they had debts to pay," she said.

Commission to focus on 'those in senior positions'

Commissioner Holmes told the inquiry it will focus on those in senior positions who had oversight of the unlawful automated program.

"A good deal is known about how the Robodebt scheme operated, but not much has been revealed about why, about what advice or consultation or reasoning or response to criticism was occurring behind the scenes at any stage," Commissioner Holmes said.

"The focus, appropriately and in accordance with the terms of reference, will be on those in senior positions who had or should have had oversight of it," she said.