Mercilus, who was released by the Houston Texans on Tuesday after spending 10 seasons with that franchise, turned down more money elsewhere to join Green Bay’s defense, the source said.
The Kansas City Chiefs were also in the mix for Mercilus, who had guaranteed money owed to him as part of his Texans deal, a source told Fowler.
Mercilus fills a need for the Packers as linebacker Za’Darius Smith has been sidelined for most of this season with a back injury.
The Texans drafted Mercilus, 31, in the first round in 2012, but this was his first year in Lovie Smith’s defense, which saw him move from outside linebacker to defensive end.
In six games for Houston this season, Mercilus has three sacks, four tackles for a loss, three quarterback hits and 12 tackles.
His 57 sacks in 10 seasons for the Texans rank second in franchise history behind J.J. Watt, who had 101 sacks with Houston.
ESPN’s Sarah Barshop contributed to this report.