Kordia Group chief executive Scott Bartlett will take a period of extended leave to focus on his health, effective immediately.
The move follows a recent diagnosis of multiple tumours on the brain, of which treatment is currently underway.
Kordia Group chief financial officer Shaun Rendell will take over as acting CEO in the interim, the state-owned cyber-security and telecommunications company said in a statement.
Rendell expressed his sympathies and well-wishes for Bartlett in the wake of his leave.
"We all have a huge amount of love and respect for Scott. The entire team wishes him the best of luck for his journey ahead, and we look forward to seeing him back in the office soon.
"At Kordia, we've always taken the view that the health and wellbeing of our people comes first, and we're fully committed to supporting Scott during this difficult time.
"For our customers, it's very much business as usual and we remain fully focused on ensuring they continue to receive the best service, advice and support," Rendell said.
Bartlett notched up three years as Kordia Group chief executive earlier this month.