Radio NZ reports:
Mr Groenewald told the ABC he was not happy with the way the Fiji military was interfering with policing.
The South African took up the job in May last year.
His departure was indirectly due to a standoff with the military over policing matters, he said.
Mr Groenewald, who described himself as a true-blooded policeman, said he was not satisfied with the way they interfered.
In a statement, the Fiji government said Mr Groenewald was leaving for personal and family reasons.
Following advice from the Prime Minister as the Chair of the Constitutional Offices Commission, the President had appointed Colonel Sitiveni Qiliho as the Acting Commissioner, the government said.
I had high hopes for Fiji after their election and new constitution. But this is disturbing.
Having the Police Commissioner resign due to military interference is bad enough. That suggests the military may see themselves as still above the law.
But to then appoint a military officer as the Acting Commissioner is worse.