Wiley, the top pass rusher on the market, agreed Sunday to the deal, which includes a $9 million signing bonus. An unrestricted free agent, Wiley replaced Bruce Smith in the Buffalo Bills' lineup last year and responded with 10 1/2 sacks.
The deal caps a $55.5 million weekend spending spree by new general manager John Butler, who is trying to turn around a team that was an NFL-worst 1-15 last year.
On Saturday, the Chargers signed free agent cornerback Ryan McNeil to a $15.5 million, five-year deal, including a $2.5 million signing bonus.
Wiley, who's from Compton in the Los Angeles area, is due in San Diego on Monday to take a physical and sign the deal, his agent, Brad Blank, said from Boston.
When he was GM of the Bills, Butler picked Wiley in the second round of the 1997 draft out of Columbia.
"I want to give John Butler all the credit in the world, but the proximity to Los Angeles was huge," Blank said. "Personally, I'd like to keep him on the East Coast, but he's been away from home for a long time."
Chargers officials didn't immediately return phone calls. Wiley was expected to hold a news conference Monday, Blank said.
Chargers line coach Wayne Nunnely was excited to hear the news. Wiley will play opposite Raylee Johnson, who had 10@1/2 sacks in 1999 before suffering a season-ending knee injury in an exhibition game in August.
"That is real big," Nunnely said. "With him and Raylee on the edges, that really gives us a boost in terms of our pass rush, and they're two guys who can still play the run."
Wiley visited the Chargers on Friday and said he wasn't scared away by their awful 2000 season.
"They really have a firm confidence in their situation going up, especially with John Butler here," Wiley said after his visit.
But Wiley also was disappointed that he left town without receiving an offer, Blank said.
Blank said he was watching the undercard bouts before the Evander Holyfield-John Ruiz heavyweight fight on TV Saturday night and grew bored.
"So I called John Butler and gave him a pep talk that he (Wiley) wanted to be here," Blank said. "I told him Marcellus was frustrated when he left without an offer and John said he didn't realize that."
Wiley had been scheduled to visit the Oakland Raiders on Monday an might have gone to Cincinnati later in the week.
"He knew were he wanted to end up and didn't want to drag out the process if he could get something done," Blank said.
The Chargers' previous biggest deal was Ryan Leaf's rookie contract that potentially was worth $31.25 million over five years, including a club-record $11.25 million signing bonus. Leaf made about $12.3 million in his troubled three seasons in San Diego. He was waived on Wednesday and claimed by Tampa Bay on Friday.
Last fall, All-Pro linebacker Junior Seau received a new contract worth about $32 million over five seasons.
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