Financial terms of the deal weren't disclosed.
Miller, one of the top blockers among NFL tight ends, had one season remaining on the five-year contract he signed after being Pittsburgh's first-round draft pick in 2005.
Miller, 26, has played on two Super Bowl-winning teams in his first four NFL seasons. He caught 48 passes for 514 yards and three touchdowns last season after catching 47 passes in 2007.
The 6-foot-5, 256-pound Miller has 168 catches for 1,932 yards, an 11.5 yards per reception average, and 21 touchdowns during his career. He also has three touchdown catches in the playoffs.
The Steelers chose to sign Miller before training camp begins Friday instead of waiting to see if there will be a new NFL labor agreement. If there is no new deal, and 2010 is an uncapped season, the Steelers could have retained Miller by making him a tender offer after this season, but they chose instead to negotiate a new contract.
Copyright 2009 by The Associated Press