A source said the four-year deal is worth $15 million. The 6-foot-4, 232-pound defenseman, who has 127 points in 298 career NHL games, was an unrestricted free agent.
Johnson, 24, led all Colorado defensemen in scoring this past season with 26 points in 73 games. He also led all team blueliners in assists and shots on goal (155).
The first overall pick in the 2006 entry draft, Johnson was acquired by Colorado from St. Louis on Feb. 18, 2011.
A native of Bloomington, Minn., Johnson helped the United States capture a silver medal at the 2010 Olympic Winter Games in Vancouver.