The team officially announced the one-year contract on Monday morning.
Kerrigan, 32, was a first-round pick by Washington in 2011 and played the first 10 years of his accomplished NFL career for Washington, racking up 95.5 sacks and 147 quarterback hits.
He started just one game in 2020 and played 38 percent of the team's defensive snaps -- by far the lowest of his career -- but managed 5.5 sacks and five tackles for loss.
Kerrigan has 13.5 career sacks against Philadelphia, tied for most sacks against any one team with the Dallas Cowboys.
"I know I probably wasn't your favorite player over the past decade, but Eagles fans I'm fired up to be playing for you guys now! LFG!!!" Kerrigan wrote on social media.
Kerrigan joins a defensive end rotation in Philadelphia that includes Brandon Graham, Derek Barnett and Josh Sweat. He'll be playing for new defensive coordinator Jonathan Gannon, who is expected to ask his linemen to read and react more, in contrast to former DC Jim Schwartz's constant attack style.
On Sunday night, Kerrigan said goodbye to Washington.
"I'll never be able to sum up what these past 10 years have meant to me in an Instagram post, but what I can say is that they have been some of the best of my life. I hope you had as much fun watching me as I did playing for you. Thank you, Washington, for everything," Kerrigan said.
ESPN contributed to this report.