The first day of three weeks of hearings will begin on Monday, with the former chiefs of staff to two former ministers due to appear.
Megan Lees, the former chief of staff to then human services minister Marise Payne, and Charles Wann, the former chief of staff to Scott Morrison when he was social services minister will give evidence.
They will appear on Monday alongside two lead plaintiffs in the robodebt class action lawsuit, as well as people who were affected by robodebt.
The scheme ran from 2015 until 2019, which recovered $750 million from 380,000 people using annual tax office data to calculate average earnings.
Robodebt was allowed to operate for several years despite concerns it was unlawful, with some taking their own lives while being pursued for debt.
The fourth block of hearings will also examine the inquiry by the Commonwealth ombudsman into the scheme, proposals to expand robodebt, the impact robodebt had on victims as well as how the scheme was wound up.
Three expert reports will also be introduced during the hearing block, including a review of the data matching processes as well as changes that could be made within the federal public service following evidence presented the royal commission.
Commissioner Catherine Holmes last week wrote to the government requesting a two-month extension of the commission.
The final report will be handed down by the end of June this year, rather than the original deadline of April.
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