The 25-year-old Stubbs, who captained Sunrisers Eastern Cape to a third SA20 title in four seasons in January, will join up with Hampshire for the Blast immediately after the IPL ends in May.
He will then spend close to three months in Southampton to complete his duties in the Hundred as the Proteas have a large gap in the international calendar.
"Tristan is a hugely talented player with strong connections to the club through his time at Delhi Capitals and his relationships with our coaches, past and present," Giles White, Hampshire's director of cricket, said.
"He's a wonderful addition, and having him involved is a massive boost for both our squad and the competition as a whole. We can't wait to see him light up the Bowl."
Stubbs worked closely with former Hampshire head coach Adi Birrell at Sunrisers Eastern Cape and Russell Domingo (assistant coach), with Domingo succeeding Birrell as Hampshire's head coach next season.
Stubbs was one of four direct signings by Southern Brave's men before next month's inaugural Hundred auction, along with Jofra Archer, Jamie Smith and Marcus Stoinis.
Tristan Stubbs says he is excited to have an opportunity to play and work on one format of the game as he eyes hitting prime form for the Proteas at the T20 World Cup early next year.
England batter Jacob Bethell conceded his decision to skip some domestic cricket meant he wasn't able to perform at his best when called upon at international level.
South Africa clinched a dramatic five-run victory over England at Lord's to secure the one-day international series with a game to spare.
Proteas Tristan Stubbs and Faf du Plessis were dismissed cheaply for the Delhi Capitals as they failed in their run chase against the Mumbai Indians in the IPL on Wednesday night.
