Tonga's police commissioner, Chris Kelley, says he's disappointed that the government hasn't offered him the two years right of renewal he'd negotiated in his orginal contract.
The New Zealander finishes on Friday after three years in the post.
He had been brought in as part of a foreign aid funded rehabilitation of the police force following the riots in 2006 in which it'd proven to be ineffectual.
Mr Kelley says he's been given no explanation for why the right of renewal hasn't been offered.
"I acknowledge and accept the right of the government to employ who they wish but they certainly haven't given me anything in writing or even verbally. my understanding is that they have had some concerns over the new Police Act,, but I certainly haven't been given any reasons."
The Tonga police minister, Viliami Latu, says the government believes the time is right for a local to re-assume command of the force.
He says the swift introduction of the Police Act, which allowed for significant changes including merit based promotion, was a factor in their decision.