Kevin S. O'Leary, 55, pleaded guilty to second-degree murder Tuesday in U.S. District Court in Seattle.
O'Leary said he smothered his wife, Valerie Jefferson, while they were arguing about an affair he had 10 years earlier, and he wrapped her body in a blanket and hid it under the bed. Police found her remains five days later.
Prosecutors agreed to recommend a sentence of no more than 15 years in prison.
Federal prosecutors had jurisdiction over the case because the killing occurred on tribal land.