Penn fills the opening created when Jared Veldheer left as a free agent for Arizona and left unfilled when Rodger Saffold failed his physical after agreeing to a five-year, $42.5 million deal with Oakland.
NFL Network reported that Penn's contract is worth $9.6 million with $4.2 million guaranteed.
Penn, who turns 30 next month, was released earlier this month by Tampa Bay after the Buccaneers signed Anthony Collins to a five-year, $30 million contract to take over at left tackle.
''I had a chip on my shoulder from when the season ended this past season, because I feel like I was coming off one of my worst seasons of my career,'' Penn said. ''They just added more fuel to the fire, the Bucs releasing me. I do have a big chip on my shoulder, and I am ready to get back at it. I wish the season started in a month.''
Penn struggled in pass protection last season with Tampa Bay, allowing 12 sacks, including nine in the final six games, according to Pro Football Focus. Only one tackle - Will Beatty of the Giants - was blamed for more sacks last season. Penn also allowed 28 quarterback hurries and six quarterback hits and ranked in the middle of the pack in terms of total pressures allowed.
Penn was more successful as a run blocker - an area where the Raiders needed improvement this offseason.
Penn said he didn't want to make excuses but blamed the instability of the franchise in Tampa Bay under former coach Greg Schiano and the change at quarterback from Josh Freeman to Mike Glennon for some of his problems.
''I had six different guards throughout the year playing next to me, two different quarterbacks and it's just tough,'' Penn said. ''Playing from behind a lot and stuff like that. A lot of stuff went into it, but that is the past. I am ready to move on, and I am looking forward to turning this thing around this season coming up.''
He has played in 122 career games over his eight seasons with Tampa Bay, including 108 consecutive starts at left tackle since 2007.
Penn visited Oakland last week but left without signing a deal. He then met with the Washington Redskins about playing right tackle before finally signing with the team he cheered for as a kid growing up in Southern California.
Penn was also excited about a reunion with Oakland offensive coordinator Greg Olson, who had that position for three seasons in Tampa Bay.
''I wasn't ready to play right tackle yet,'' Penn said. ''I feel like I am a great left tackle.''
The Raiders have placed a high priority in free agency on upgrading the offensive line, having also reached deals with right tackle Austin Howard and interior lineman Kevin Boothe. They also re-signed Khalif Barnes before he hit the open market.
The Raiders had little continuity on the line last season as injuries and poor play forced Oakland to use eight different starting line combinations.
Oakland also announced that safety Usama Young officially signed the two-year deal he agreed to last week to return to the Raiders.
Young joined Oakland last season on a one-year deal with expectations of becoming the starting free safety. But a little more than a month after signing Young, the Raiders signed Charles Woodson to a one-year deal to fill that spot.
Young moved into a backup role and played well when he got his chance on defense and special teams. He started once in his 12 games before being placed on injured reserve with a neck injury in December.
The 29-year-old Young had one interception, three passes defensed and 2 1/2 sacks last season with the Raiders, playing about one-quarter of the defensive snaps when healthy.
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