Miller, the team's first-round draft pick in 2005, would have entered the final year of his contract had he not agreed to the extension.
It was also a possibility that Miller could've remained a restricted free agent next March, considering the unresolved status of the league's procedural agreement with the players' union.
The 6-5, 256-pound Miller will turn 27 on Oct. 22. In four regular seasons, he's caught 168 passes for 1,932 yards and 21 touchdowns. In playoff games, Miller has 26 catches for 348 yards and 3 touchdowns.
Last regular season Miller caught a career-high 48 passes for 514 yards and 3 touchdowns.