Garafolo reported the contract includes another $2 million in incentives.
Joseph appeared in 13 games for the Minnesota Vikings in 2019, finishing with 44 tackles, three sacks and one forced fumble.
The 31-year-old reached back-to-back Pro Bowls in 2016 and 2017, but his performance has dipped a bit since then.
The Vikings released him and cornerback Xavier Rhodes last week prior to the start of the free agency negotiating window. Together, the moves saved Minnesota about $18.6 million in salary cap commitments for 2020.
Pro Football Focus' Steve Palazzolo provided a brief rundown on Joseph after he hit the open market:
"Joseph was once one of the best all-around nose tackles in the league, but he's coming off his worst PFF grade (69.5) since 2011. He's only totaled 18 pressures in each of the last two seasons despite rushing 347 times last year and 363 times in 2018, and that low pressure rate will limit his future opportunities. Still, Joseph could play a role as a one-down run-stopper, though that part of his game has also regressed last year, as his 66.3 run-defense grade in 2019 was his worst since 2012."
The Chargers won five games in 2019 and will have to replace Philip Rivers, who agreed to a one-year, $25 million deal with the Indianapolis Colts, per NFL Network's Ian Rapoport. With the addition of Joseph, Los Angeles is clearly aiming for the playoffs in the upcoming season.
The team has pressing needs elsewhere on the field—particularly along the offensive line—but Joseph addresses what was a weakness in 2019.
The Chargers' defensive line was 20th in adjusted line yards and 25th in adjusted sack rate, per Football Outsiders. They allowed the fourth-most adjusted line yards (4.89) through the interior, underscoring how much they needed to strengthen at defensive tackle.