Tiatia, who played two Tests for New Zealand in 2000, was the forward coach under Hammett in the team's debut season this year.
He has also been assistant coach of Ospreys in Wales and the Japan national team.
Tiatia said he was excited to take over as head coach and build on the work done by Hammett in establishing the Sunwolves.
"Next season is going to be a continuous process from the first season, but also we have to face new challenges and improve some areas further," he said.
The Sunwolves finished last in the 2016 Super Rugby tournament, with only one win from 15 games.
