General manager Stan Bowman says the team expects "immediate" contributions from the 34-year-old Turco, who's played in the NHL for 10 seasons, all with Dallas. He is a three-time all-star.
Niemi helped the Blackhawks win the Stanley Cup this past season after earning US$826,875 as a rookie. He was awarded a $2.75 million salary for next season by an arbitrator, putting Chicago in a tough spot to stay under the NHL's salary cap.
The deal with Turco was announced Monday. Niemi becomes the eighth player to leave the Blackhawks since the season ended.
Turco had worked privately with GDI's Cheif Goaltending Consultant Ian Clark in preparation for the 2009/10 NHL season.