Mr Truss will address the Nationals party room on his retirement schedule shortly before his statement to the House of Representatives at 12.30pm.
Prime Minister Malcolm Turnbull will also make a statement following Mr Truss.
Agriculture Minister Barnaby Joyce is expected to be elected the new leader of the Nationals at a partyroom meeting on Thursday night.
This comes one day after Trade Minister Andrew Robb confirmed he was calling it quits.
Mr Robb on Wednesday announced he won't contest the next election, saying he felt the time was right to leave politics and hand over the baton to the next generation in the Liberal Party.
He believes the Turnbull government is in "great shape" and no longer requires his assistance.
Prime Minister Malcolm Turnbull hailed Mr Robb the most successful trade minister in the country's history, noting three "enormous" free trade deals with China, Japan and Korea signed on his watch.
The prime minister also pointed to his work securing the Trans-Pacific Partnership, a historic trade agreement between 11 countries including the United States and China.
Mr Robb, 64, has ambitions to work in the private sector and mental health and doesn't want to leave it too late.
"I'd be 68, 69 after the next term, and I felt that was leaving it too late," he told ABC's 730 on Wednesday evening.
But he won't be leaving the ministry in a hurry, confirming the prime minister wanted him to stay on potentially for some months.
The pair's announcements will provide Mr Turnbull an opportunity for a major ministerial reshuffle.
He already has to fill two ministerial seats in the wake of scandals claiming the scalps of Jamie Briggs and Mal Brough, with a cloud over another minister, Stuart Robert.
The human services minister is the subject of an inquiry - which could report back as early as Thursday - into whether he breached ministerial standards by helping a friend and Liberal Party donor sign a mining deal in China in 2014.
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