Niemi became the Chicago Blackhawks starter midway through the 2009 season and went 26-7-4 in 39 games with a 2.25 goals-against average and seven shutouts.
"Antti's play last season speaks for itself," Sharks general manager Doug Wilson told reporters. "Our goal this summer was to create the best goaltending unit we could and we feel we have successfully done that."
The 27-year-old Niemi became a restricted free agent on July 1, and took the Blackhawks to arbitration when the two sides could not reach agreement on a contract.
An arbitrator awarded Niemi a $2.75 million salary, and Chicago exercised its right to walk away from the award, making the goaltender an unrestricted free agent.
(Reporting by Mike Mouat in Windsor, Ontario. Editing by Steve Ginsburg; To query or comment on this story email firstname.lastname@example.org)