Smit has spent the last five seasons with Sharks but, as expected, he has now agreed a move to England.
He confirmed his new destination via Twitter, writing: "It's official, I proudly announce today that I'll be joining Saracens once this season is over for 2 seasons and look forward to a new chapter."
Smit, 33, also spoke about his decision to end an 11-year Springbok career after next year's tournament in an interview with the Daily Telegraph.
He said: "I am hoping to make it to the World Cup and have a pretty good shout there and that will be me," said Smit.
"I have had 11 years with the Boks so I think I have had my fair share and that will allow me to concentrate fully with Saracens, when I link up with them two weeks after my last game [for South Africa], which will hopefully be early part of November.
"My intention is to go to Saracens and make a big impact. My body is strong and that is why I have signed for another two seasons.
"I have been lucky that my body has held up pretty well and I do feel I can make a difference and fulfil my role within a team.
"My job is to fit in as fast as possible, earn the respect of the players and immerse myself in the culture."
Hooker Smit is likely to fall behind compatriot Schalk Brits in the Sarries pecking order, despite the latter missing out on selection for South Africa recently.
Smit is aware of the competition he faces at his new club and sympathises with Brit's World Cup disappointment.
"Schalk Brits is one of their best players and my role there will be probably to relieve the pressure on him a bit and hopefully bring through some of the younger players," Smit said.
"It is probably a little frustrating for him (to be overlooked by the Springboks) but his cause probably hasn't been helped by the fact that we had to pick overseas players like Ruan Pienaar and Francois Steyn as most teams don't like to pick too many players abroad."
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