No dollar figure was disclosed by the reigning Super Bowl champions, but the Pittsburgh Post-Gazette said he would get $35.3 million in the next six years with a $12.5 million signing bonus.
Miller, 26, one of Pittsburgh's best blocking receivers, was eligible to become an unrestricted free agent next March.
He set career highs in 2007 with 566 receiving yards after 47 receptions with seven touchdowns, and last season, he caught 48 passes for 514 yards, scoring three touchdowns.
In four NFL seasons, the 6-5, 256-pound Miller, a former all-American at the University of Virginia, has scored 21 touchdowns after 168 receptions for 1,932 yards.
He was scheduled to earn $900,000 this season with a $750,000 roster bonus.