Peterborough-born Olver, 22, becomes Warriors' fifth pre-season signing ahead of the 2017-18 campaign.
He makes the same move as Saints prop Ethan Waller, who signed in January, while Wasps winger Tome Howe and Jersey forwards Pierce Phillips and Simon Kerrod agreed terms in February.
Olver will be competing for a place next season with Ryan Mills and Tom Heathcote, who have signed new deals.
But although he has largely played at stand-off, Mills has already indicated that his preferred position is at inside centre.
"Sam is a hungry young player who will provide further competition for the number 10 jersey," said Warriors director of rugby Gary Gold.
"He has experience of working alongside some top-class fly-halves and we're looking forward to seeing how he develops."
Olver, capped both at Under-18 and Under-20 level by England, first signed a professional contract at Franklin's Gardens in March 2013, since when he has made 13 first-team appearances.
He also spent time on dual registration at Moseley, for whom he played against Warriors in their Championship promotion-winning season.
Worcester Warriors have signed fly-half Sam Olver from Northampton Saints.