The 6-foot-6, 262-pound Ellis, who turns 34 on Aug. 14, was released earlier this month by the Dallas Cowboys -- his team for all 11 of his NFL seasons. The sides completed the deal late Monday when he signed the contract, Raiders CEO Amy Trask said.
Ellis has also played linebacker but will be a defensive end in the Raiders' 4-3 system. Oakland's defense struggled in the pass rush and to generate sacks last season. Training camp opens next month in nearby Napa.
"We are proud and excited that he chose the Raiders," Trask said by phone. "We believe he will be a fine contributor at defensive end."
Raiders coach Tom Cable has acknowledged the team might trade former Pro Bowler Derrick Burgess, who is unhappy with his contract, if Oakland gets adequate compensation.
Ellis has 77 career sacks, including a career-best 12½ in 2007 for the Cowboys. He's had 30 or more tackles in eight of his professional seasons.
Burgess heads into the final year of a deal that pays him a $2 million base salary this season. The Raiders have shown no interest so far in renegotiating or extending the contract.
Oakland finished 5-11 last season and went 4-8 under Cable, who took over for the fired Lane Kiffin on Sept. 30. Cable had the interim tag removed from his title in February.