The 30-year-old World Cup winner will join the Sharks from next season and has committed until 2013.
Smith, a former Melbourne player, is the second high-profile signing by the Sharks in recent weeks after the club landed Penrith youngster Wade Graham.
“This is fantastic news for our club and Jeremy will be a tremendous asset both on and off the field,” Flanagan said.
“He is a quality player, who has a vast amount of experience and he will really bolster our forward pack.”
“He has played at an international level along with quality clubs like Melbourne and St George with great commitment and desire… he is definitely a player who can make a huge difference to our team.”
Smith, a former New Zealand player of the year, has missed a large chunk of 2010 due to injury but has experience of two Grand Finals with Melbourne and will add experience to the Sharks’ squad.
“He’s big, strong and tough and has great experience in the big game environment,” Sharks General Manager of Football, Darren Mooney, said.
“This club is about developing our local juniors to first grade but it is also great to attract a high quality athlete like Jeremy.
“It’s a massive boost for the club and moving forward we are very excited about him wearing the black, white and blue.”