Roos penned a one-year, two-way contract with Ottawa on Tuesday.
Roos was limited to just four NHL games for the Blackhawks last season, registering zero points, two shots and eight hits while averaging 14:44 of ice time. While he likely faces an uphill battle, the 25-year-old Swede should at least have a chance of making the Opening Night roster as a third-pairing defenseman.