Eight NFL teams dismissed their head coach at the end of the regular season and Jacksonville and Arizona were the last of those teams to fill the vacancies.
Jacksonville announced early in the day that Bradley would replace Mike Mularkey, who was fired last week after a 2-14 season.
Bradley has spent the last four seasons as defensive coordinator for the Seattle Seahawks. New Jacksonville General Manager Dave Caldwell had reportedly interviewed Jay Gruden and Brian Schottenheimer before settling on Bradley.
"It was just a matter of time before Gus Bradley became a head coach in the NFL," Caldwell said. "And the Jacksonville Jaguars are extremely fortunate that Gus will be on our sidelines for many years to come."
Seattle had the No. 1 scoring defense in the NFL this season, giving up 15.3 points a game. The Seahawks narrowly missed out on a berth in the NFC Championship game when they fell to Atlanta 30-28 in last week's round of playoff action.
ESPN reported that Arians had been given a four-year deal to coach the Cardinals, replacing the fired Ken Whisenhunt.
Arians also replaced Whisenhunt as offensive coordinator for the Pittsburgh Steelers when Whisenhunt left that position in 2007 to go to Arizona. Arians spent last season as offensive coordinator for the Indianapolis Colts and was the interim head coach while Chuck Pagano was undergoing treatments for leukemia.
The Colts went 9-2 under Arians.
Buffalo, Cleveland, San Diego, Kansas City, Philadelphia and Chicago have also undergone coaching changes since the end of the regular season. One of the dismissed coaches, Philadelphia's Andy Reid, was then hired to guide Kansas City.
Buffalo hired Doug Marrone, Cleveland chose Rob Chudzinski, San Diego selected Mike McCoy, Chicago went with Marc Trestman and Philadelphia was able to land Oregon Coach Chip Kelly.
Two of the head coaches who lost their jobs -- San Diego's Norv Turner and Whisenhunt -- were both hired Thursday. Turner is the new offensive coordinator for Cleveland and Whisenhunt will fill the same job with San Diego.