Penn agreed to a two-year, $9.6 million deal with $4.2 million guaranteed, a source told ESPN NFL Insider Adam Caplan.
Penn, 30, played in 112 games for the Buccaneers, including 108 consecutive starts, the fourth-longest such streak in franchise history. He was released by Tampa Bay last week after the Buccaneers reached an agreement with former Cincinnati Bengals offensive tackle Anthony Collins on a five-year deal worth $30 million.
Penn is likely to step in as the Raiders' new starting left tackle. The Raiders had previously made a deal with Rodger Saffold to be the team's left tackle, but it fell apart when Saffold failed his physical.