The trade, which sent Oakland's seventh-round draft pick in 2012 and a conditional fifth-rounder in 2013 to Seattle, was completed Thursday after Curry passed a physical.
A day after cleaning out his locker with the Seahawks, Curry posted a picture of himself wearing a Raiders shirt and hat on Twitter.
It's uncertain where Curry will fit into Oakland's defense. Middle linebacker Rolando McClain was limited in practice due to an ankle injury, while defensive end Matt Shaughnessy is sidelined by a shoulder injury.
A strongside linebacker with the Seahawks, Curry gives Oakland the flexibility to move outside linebacker Kamerion Wimbley to the defensive line to replace Shaughnessy if need be.
"(Curry) is athletic. He can run, he tackles, he takes on linemen, he takes on backs," coach Hue Jackson said before the deal was completed. "I feel very comfortable in my evaluation, watching tape of this young man and what he is and what he could do for us. I like this situation of him being a part of our football team."
Jackson brushed aside criticisms of Curry, who went from being a can't-miss prospect in Seattle to a backup on defense after losing his starting spot to K.J. Wright.
"I can't speak to what went on up there but I know what's going to go on here," Jackson said following practice, before the deal was completed. "We came to a collective agreement over the last couple days of myself watching tape and feeling very comfortable about the opportunity to improve the football team."
The move is the first by the Raiders since the death Saturday of owner Al Davis.
Jackson, who said Davis trained him to make personnel moves, declined to discuss details of the deal until it was finished. Curry is signed through the 2012 season but it's believed he agreed to restructure parts of his contract before trade was completed.
Curry's arrival gives the Raiders 12 former first-round picks, seven on defense.
The No. 4 overall pick in 2009, Curry never lived up to pre-draft expectations in Seattle after winning the Butkus Award as a senior at Wake Forest. The 6-foot-2, 255-pounder has 5½ career sacks and only 22 tackles this season after losing his starting job.
Curry's struggles reached a low point in Seattle's 35-26 win over the New York Giants last Sunday when he was replaced in pass coverage by David Vobora, who had been re-signed by the Seahawks earlier in the week.
Seattle general manager John Schneider released a statement Thursday addressing the trade.
"On behalf of Mr. (Paul) Allen, coach (Pete) Carroll, and the entire Seahawks family, we want to thank Aaron for his contributions to the Seahawks and wish him all the best with his fresh start in Oakland."
McClain did not practice Wednesday and was limited in workouts on Thursday. If he can't play in Sunday's home game against Cleveland, the Raiders are expected to start Darryl Blackstock.
Curry could provide insurance behind Blackstock in the middle but Jackson sounded as though the Raiders plan to leave him on the outside for now.
"I don't want to put him in a whole bunch of spots," Jackson said. "I want to let him play one thing and let him become great because I think the guy has great talent."
A team official announced that the game has been sold out, marking the first time since 2008 that the Raiders have sold out three consecutive home games. Team officials have planned a tribute to Davis for the game and several former players are expected to take part.