The team announced the deal Thursday.
Niemi stopped 129 of 136 shots in the Western Conference final to help Chicago sweep the Sharks. The Blackhawks went on to win the Stanley Cup behind Niemi but cut ties with the goalie because of salary cap concerns.
The 27-year-old Niemi played all but one period of the Blackhawks postseason run, going 16-6 with a 2.63 goals-against average, .910 save percentage and two shutouts.
He was awarded a $2.75 million salary in arbitration. Chicago chose to let him go and signed veteran Marty Turco.