Stokley played in all 16 games last season for Denver but had just 19 catches. Two years ago, when current Seahawks offensive coordinator Jeremy Bates was the Broncos offensive coordinator, Stokley had 49 receptions, second most in his career.
Stokley, 34, was released by the Denver Broncos on Sept. 14 after reaching an injury settlement with the team. The Broncos had placed Stokley on injured reserved on Sept. 4 with a groin injury.
The Seahawks believe he can become an effective slot receiver, and he has familiarity with the offense from his active time in Denver under Bates.
Stokley caught 108 passes for 1,490 yards and 12 touchdowns in three seasons with the Broncos. For his career, he has 307 receptions for 4,319 yards and 34 touchdowns.
Barbre started seven games for Green Bay last year, while Giacomini was signed from the Green Bay practice squad.
Chris Mortensen is ESPN's senior NFL analyst. Information from The Associated Press was used in this report.