Included in the deal is $10 million in guaranteed money, the source said. The Steelers announced the deal Tuesday but did not give financial details. Starks is signed through 2012.
The agreement between the Steelers and Starks ends a two-year stretch in which Starks, a transition player in 2008 and the franchise player in 2009, ate up a lot of Pittsburgh's cap room.
By getting a long-term deal, Starks was able to get a good read on his future. Even though the Steelers gave him the transition tag in 2008, he didn't open the season as a starter.
"We were very fortunate to have him," Steelers director of football operations Kevin Colbert said, according to The Associated Press. "A transition on a backup probably didn't make a lot of sense, but we didn't feel like we would have been as good a team without him. We wanted to do a long-term deal [in 2008] but we couldn't get it done."
Left tackle Marvel Smith's back problems led to Starks getting the chance to be the left tackle in the second half of last season. The 6-foot-8, 345-pound Starks remained at left tackle through the Super Bowl.
Starks had been an unsigned franchise player with an $8.451 million tender. His agreement is expected to save the Steelers about $3 million in salary-cap space.
The 27-year-old Starks started 45 games during his first five seasons in Pittsburgh. He was a third-round draft pick of the Steelers in 2004.
John Clayton is a senior writer for ESPN.com.