The 25-year-old made 39 first-team appearances for the club, including 19 in the Guinness Premiership this season. Harding is now expected to return to New Zealand in the coming weeks to continue his rugby career.
Utility back Whatling, 22, is a product of the Warriors Academy and has been at Sixways for the last three years.
The former England Under-21 skipper made seven first-team starts last season, including three in the Guinness Premiership where he scored a memorable try against Leicester Tigers at Welford Road.
Harding and Whatling join Thomas Lombard and Miguel Avramovic as players who have left Warriors since the end of last season.
Mike Ruddock, Warriors Director of Rugby, said: "I would like to thank both players most sincerely for their efforts for Worcester.
"Simon has been unfortunate with injuries and the arrival of Sam Tuitupou next season means his chances would have been limited. He leaves the club with our very best wishes for the future.
"Tom had expressed a desire to return home and although we would have liked him to stay we respect his wishes and hope he has every success in his career.
"We are now looking for potential replacements and at this moment I am considering the quality of players in our Academy programme as well as the possibility of bringing in replacements externally."