Smith signed with the Packers on Thursday, with his agent, Doug Hendrickson of Wasserman, telling ESPN's Adam Schefter it is a one-year deal.
The move came a day after news broke that the Packers were a potential suitor for Gilmore shortly before he was traded from the New England Patriots to the Carolina Panthers for a 2023 sixth-round draft pick. But the Packers did not have enough salary-cap space to acquire Gilmore in a trade because they would have to inherit the remaining $5.8 million of his base salary on this year's salary cap. The Packers started Thursday with about $6.5 million in cap space and still need room for the in-season moves that injuries might necessitate.
Smith, however, fits under the cap because the Cowboys are on the hook for the entirety of his $7.2 million base salary this season as a result of veteran termination pay rules.
He filled the roster spot of outside linebacker Chauncey Rivers, who was placed on injured reserve. Rivers tore an ACL on the second-to-last play of practice Wednesday, a source told ESPN.
"Nothing's official yet, but I go back a long time with Jaylon," Packers coach Matt LaFleur, who coached Smith at Notre Dame, said before the signing was announced. "I've always had a lot of respect for him, not only as a football player but as a man. He was one of my favorites when I was at Notre Dame. I just think a veteran guy who's played at a really high level and just can bring kind of a mentality and leadership to our defense.
"Certainly, he's going to be behind quite a bit, being the fact we're heading to Week 5 and it's a totally different system, so there's going to be a lot of work that needs to be put in, not only from him but from our coaching staff to get him up to speed. But we'll let him kind of come in here and compete to play."
With the Packers, Smith could work his way into the starting lineup alongside De'Vondre Campbell, who has been one of their biggest playmakers this season, or simply offer backup depth. Second-year pro Krys Barnes opened the season as the other starting inside linebacker; he missed last week's game against the Pittsburgh Steelers because of a concussion he suffered the previous week against the San Francisco 49ers.
LaFleur said it was unlikely Smith would play Sunday at the Cincinnati Bengals.
Smith, 26, saw his role with the Cowboys diminish with the addition of first-round pick Micah Parsons, the production from Leighton Vander Esch and the return of Keanu Neal from the reserve/COVID-19 list.
Smith was a second-round pick by the Cowboys in 2016 even though they considered it unlikely for him to play for a year given the knee injury he suffered in his final college game.
He made his debut in 2017 and has played in every game since.