Sources said Asomugha is guaranteed $28.5 million in a complicated deal that features a provision in which the entire contract can be guaranteed if the Raiders decide to keep the 27-year-old for the third season.
The seventh-year pro is one of the league's elite cover defenders. He was selected for the Pro Bowl and chosen to The Associated Press All-Pro team last season despite getting just one interception because Oakland's opponents rarely even dared to throw to his side of the field.
Asomugha made critical statements about the Raiders' direction late in their sixth consecutive losing season, but acknowledged he probably would remain with the club because of the franchise tag. His new contract and the Raiders' new coaching staff likely made the decision much easier.
This was the second major re-signing by the Raiders in two days; on Wednesday, Shane Lechler agreed to a four-year, $16 million contract, the richest ever for a punter.
Both deals were negotiated by agent Tom Condon, with Raiders owner Al Davis having significant involvement in brokering the agreements.
Senior writer John Clayton covers the NFL for ESPN.com. Information from The Associated Press was used in this report.