Hester confirmed in an Instagram post on Tuesday night that he signed with the Seahawks as they prepare for the postseason after losing returner Tyler Lockett to a broken leg.
"I guess God has another chapter in my book of life," Hester said in the post, which included a picture of his new locker with the Seahawks.
Safety Tyvis Powell, a rookie from Ohio State, was released to make room on the roster.
Hester was released from the Baltimore Ravens in December. The 11-year veteran was slowed by injuries and averaged 7.2 yards on punt returns and 24.5 yards on kickoff returns.
With Lockett sidelined last week after suffering the injury on Christmas Eve, J.D. McKissic and Paul Richardson temporarily took over on kickoff returns and Richard Sherman on punts.
The 34-year-old Hester has an NFL-record 20 returns for touchdowns, including a record 14 on punts, five on kickoffs and one on a missed field goal attempt return.
Hester scored seven touchdowns on punt returns and four in kickoffs in his first two years with the Bears in 2006 and 2007.
As a receiver, his best seasons were 51 catches for 665 yards and three touchdowns in 2008, 57 receptions for 757 yards and three touchdowns the following year and 40 catches for 475 yards and four touchdowns in 2010.
In 2014 with the Falcons, Hester caught 38 passes for 504 yards (31.5-yard average) and two touchdowns. He also had his last punt return for a touchdown that year.