The rebuilding Blackhawks announced the deal on Wednesday. Johnson's contract carries a $950,000 hit to the salary cap.
"Jack provides the team with a strong veteran presence, good size and a competitive edge," general manager Kyle Davidson said in a statement. "We're excited to have Jack join the organization and, coming off a Stanley Cup championship last year, he will strengthen our defensive group."
Johnson, the No. 3 overall pick in the 2005 draft, had one goal and eight assists in 74 games with the Avalanche last season. Johnson, listed at 6-foot-1 and 227 pounds, also skated in 13 playoff games.