Terms of Irvin's deal, which was first reported by the NFL Network, were not immediately known.
Irvin, 32, tweeted his excitement about returning to the team that drafted him 15th overall in 2012.
Shell's deal is for two years and $11 million, a source told Schefter. The 28-year-old Shell, a fifth-round pick in 2016, started 40 games in four seasons with the New York Jets and 37 over the past three years. His addition lessens the chances of the Seahawks re-signing right tackle Germain Ifedi.
Ogbuehi, 27, was a first-round pick by the Cincinnati Bengals in 2015 and spent last season with the Jacksonville Jaguars. He's made 25 career starts but none in the past two seasons. His deal is for one year and has a max value of $3.3 million, a source told Schultz.
With Seattle signing Shell, the Seahawks and Jets effectively swapped tackles with New York signing George Fant to a three-year, $27.3 million deal.
Ifedi is one of two remaining free agents on the Seahawks' offensive line along with left guard Mike Iupati. Seattle added a potential Iupati replacement on Tuesday in ex-Steeler B.J. Finney on a two-year, $8 million deal.
Irvin signed a one-year, $4 million deal with the Carolina Panthers last season to help then-coach Ron Rivera in his switch from a 4-3 to a 3-4 defense. His "dog mentality'' brought a needed toughness to the Panthers' defense early last season before injuries to key players took a toll.
Irvin recorded a career-best 8.5 sacks for Carolina in 13 games after missing the first three with a hamstring injury. No Seahawks defender had more than four sacks in 2019 as the team finished the regular season with only 28, tied for the second-fewest in the NFL.
The Seahawks have re-signed Jarran Reed and are trying to re-sign Jadeveon Clowney, who was their most disruptive defensive lineman last season. Seattle lost another defensive lineman, Quinton Jefferson, to the Buffalo Bills. Al Woods and Ezekiel Ansah are free agents.
Irvin won a title in the first of his two trips to the Super Bowl with Seattle and then signed as a free agent with the Oakland Raiders in 2016, after Seattle declined the fifth-year option on his rookie contract. He split time with Oakland and the Atlanta Falcons in 2018 before signing with Carolina in 2019.
Irvin has 52 career sacks, 301 tackles, 16 forced fumbles (3 recoveries) and 3 interceptions in eight NFL seasons. He also has two touchdowns.
ESPN's David Newton contributed to this report.