The deal includes a club option for 2013, the team said in news release. No financial terms were revealed.
The 35-year-old southpaw led the American League in saves in 2009 with 48.
His signing came one day after the Athletics finalized an $8.1 million, two-year deal with Australian-born, right-handed reliever Grant Balfour.
(Reporting by Gene Cherry in Salvo, North Carolina. Editing by Steve Ginsburg)