The talented gloveman will join his KFC BBL|07 Championship winning coach Jason Gillespie and teammate Rashid Khan for the competition, beginning in July.
Carey has been a standout for the Strikers, helping them to their maiden title with 443 runs and 14 dismissals in 2018.
After that breakout season, the 27-year-old has been capped 38 times in the white-ball formats, and now leads Australia as joint vice-captain in the ICC Men’s Cricket World Cup which began last night.
Strikers and Sussex Head Coach Jason Gillespie said:
"Alex has been impressive opening the batting for the Strikers in the Big Bash and now he's getting experience in the middle order with Australia.
"He can certainly clear the ropes but he's also able to read and adapt to different conditions. That versatility will give us options on how best to utilise his batting in this year's Blast. Alex is also a world-class keeper so to have a player like him joining the Sharks is a real coup for the club.
"I know Alex well from the Adelaide Strikers and he knows Sussex well from his time playing league cricket in the county, so I've no doubt he'll fit in nicely in our dressing room."
Carey and Rashid will square off when Australia play Afghanistan in their first World Cup match, starting tomorrow night from 10pm (ACST).