The Hurricanes had spoken with Hainsey in July, but were unable to sign him due to salary cap restraints, which dissipated after Pitkanen's injury was revealed.
"Ron is an experienced, two-way defenseman," said Hurricanes GM Jim Rutherford. "He was very interested in joining our team this summer, and was patient as we waited for updated information about Joni Pitkanen's injury. We are happy to be able to solidify our defense with a player of this caliber at this stage."
Hainsey, 32, collected 13 assists and 10 penalty minutes in 47 games with the Winnipeg Jets last season, his 10th in the NHL.
The Bolton, CT, native has totaled 34 goals and 158 assists for 192 points in 591 career NHL games with Montreal, Columbus and Atlanta/Winnipeg.
He was originally selected by the Canadiens in the first round, 13th overall, of the 2000 NHL Entry Draft.