The Seahawks instead opted to sign Austin Davis, who backed up Russell Wilson for one season before joining the Seahawks' coaching staff.
Kaepernick started 58 games for the 49ers from 2011 to 2016, leading the San Francisco 49ers to an appearance in the 2013 Super Bowl and an NFC Championship appearance against the Seahawks in 2014.
Before a preseason game Aug. 14, 2016, Kaepernick gained national attention when he decided to protest during the national anthem.
Later in the preseason, Kaepernick told reporters: "I'm going to continue to stand with the people that are being oppressed. To me, this is something that has to change. When there's significant change and I feel that flag represents what it's supposed to represent, and this country is representing people the way that it's supposed to, I'll stand."
His protest drew both support and backlash from many, sparking ongoing conversations that continue today.
During Week 3 of the 2017 NFL season, many NFL players opted to protest in a show of unity amid criticism from President Donald Trump.
Trump slammed players opting to protest during the national anthem, saying: "Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, you'd say,: 'Get that son of a bitch off the field right now. Out! He's fired.'"
Kaepernick and former teammate Eric Reid filed a grievance through the NFL Players Association against the NFL on Oct. 16, 2017, accusing owners of colluding to keep them out of the league.
The grievance was settled in February, but terms were not released.
Reid was ultimately signed by the Carolina Panthers.
In 69 career games, Kaepernick completed 59.8% of his passes with 72 touchdowns and 30 interceptions.
He also added 375 carries for 2,300 rushing yards and 13 touchdowns.
Since he last played in the NFL, Kaepernick has gone on to become a social activist.
Most recently, he spent his 32nd birthday feeding and helping the homeless in Oakland.
The Seahawks are on a bye this week and next play the Philadelphia Eagles on the road Nov. 24.