He should now be at the KC Stadium until the end of the 2017 season.
The Tongan international played every minute of Hull’s Super League campaign last season, the only player in the competition to do so.
The 27-year-old also scored 10 tries in 2014, and has crossed the whitewash three times so far this season.
Fetuli has been a great signing for us and has continued where he left of last year.
“He is a big part of the squad, not only on the field but off it too. I know he has really settled in the area and loves the club which is reflected in his performances.
“Hopefully he can be an integral part of a successful period at the club.”