He was, notably, the first player to kneel alongside former teammate (and current exile) Colin Kaepernick.
Last season, Reid started 12 of 13 games played, registering 66 tackles, two interceptions, four passes defensed and one fumble recovery.
The Panthers had a need at Reid's position, and he has a record of being a productive young player.
Reid played for the 49ers for five seasons before becoming a free agent after the 2017 season.
"We made this decision based on the fact he's a good football player", the Panthers general manager, Marty Hurney, told ESPN. "He is a physical safety with good ball skills and play-making ability".
The NFL recently failed in its attempt to have Kaepernick's grievance thrown out, with an arbitrator ruling that it will go to trial.
Special teams standout Colin Jones and rookie Rashaan Gaulden split snaps in Searcy's former spot during Sunday's 31-21 victory over the Bengals.
After news of Reid's signing emerged, Kaepernick sent congratulations via Twitter, saying, "Congrats 2 my brother. who should have been signed the 1st day of free agency".
Back in August, the 49ers also offered Reid a contract.
"I hope so", he said. "I know how he is as a talent".
Kaepernick has not played in an National Football League game since the 2016 season. That'd be great if we could add him to that role.
"I was happy for him".
Jim Trotter reported earlier Thursday morning that the 49ers had interest in signing Reid to a multiyear deal. The two players allege that the league's 32 owners conspired to keep them off the field due to their role in initial player national anthem protests during the 2016 NFL season.
Financial terms of Reid's one-year contract with the franchise were not immediately available.
According to a report by Jim Trotter, Carolina didn't even ask Reid if he plans to continue demonstrating.