Jackson previously started for the Seahawks in 2011. He completed 60.2 percent of his passes for 3,091 yards, 14 touchdowns and 13 interceptions while playing through a torn pectoral for most of the season.
After losing the starting job to rookie Russell Wilson, the Seahawks traded him to the Buffalo Bills during preseason. He was inactive for the entire season, and the Bills released him after signing Kevin Kolb and drafting E.J. Manuel.
Jackson has no chance of winning a starting job in Seattle with Wilson now entrenched, but he remains an acceptable backup and is familiar with offensive coordinator Darrell Bevell. If signed, he will compete with Brady Quinn and Jerrod Johnson for the primary backup spot.