The Seahawks got defensive end Chris Clemons and the Eagles' fourth-round choice in next month's draft.
Originally a second-round draft pick by Seattle in 2006, Tapp has 18 sacks, two interceptions, eight forced fumbles and four fumble recoveries in 65 games. He had four sacks in a game against St. Louis in 2007.
"Darryl is a very intense football player and we're happy to acquire him," Eagles coach Andy Reid said. "He plays very hard every snap. He's smart, he's a good person and he'll fit very well into our defensive scheme."
Clemons played two seasons with Philadelphia after posting a career-high eight sacks in 2007, his only season with Oakland. He has 20 sacks in 59 career games.
The Eagles were interested in Tapp when he played at Virginia Tech. The Seahawks had re-signed him on Monday.
"Darryl is an up-and-coming player in this league, in my opinion," Eagles general manager Howie Roseman said. "He's a good player and a good person, and we liked him very much coming out of Virginia Tech. We believe he'll be a good addition to our defensive line."