The 10-year veteran, who had spent his whole career with the Cardinals, joins a young secondary in Minnesota. The Vikings leaned heavily on rookies Jeff Gladney and Cameron Dantzler last season.
Peterson is the second major signing for the Vikings defense as free agency officially opened Wednesday. The team agreed to terms with nose tackle Dalvin Tomlinson on Monday.
Peterson, 30, has been named to eight Pro Bowls and is a three-time first team All-Pro.