On September 1, 2018, following Mack’s holdout through the entire preseason, the Raiders traded him, a 2020 second-round pick, and a conditional fifth-round draft pick in 2020 (condition unknown) to the Chicago Bears for 2019 (24th overall, Josh Jacobs) and a 2020 first-round pick, as well as 2019 sixth and 2020 third round selections. Shortly after the trade, Mack signed a six-year deal worth $141 million featuring $90 million guaranteed, becoming the highest-paid defender in NFL history.
On September 9, 2018, Mack made his Bears debut on Sunday Night Football against the Green Bay Packers. In the second quarter of the game, he sacked backup quarterback DeShone Kizer and stripped and recovered the ball. Later in the same quarter, he intercepted a pass from Kizer and returned it 27 yards for a touchdown. He became the first player since 1982 to record a sack, forced fumble, a fumble recovery, interception, and touchdown in one half. It was also his second time recording a sack, forced fumble, fumble recovery, interception and touchdown in a single game that dated back to week 12 of the 2016 season. In his second game with the Bears, Mack had four tackles and a strip-sack of Russell Wilson during Chicago’s 24–17 Monday Night Football win over the Seattle Seahawks. Mack continued his excellent play in Week 3, recording a strip-sack of Josh Rosen in the 16–14 win over the Arizona Cardinals, the first player to record strip-sacks in three straight games since Mack himself did it in 2016. He had a strip-sack again the following week in a 48–10 win over the Tampa Bay Buccaneers. Mack became the first player to record sacks and forced fumbles in four straight games since the Indianapolis Colts’ Robert Mathis in 2005. He is also the first player to record forced fumbles in the first four games of a season since the Jacksonville Jaguars’ Tony Brackens in 1999. On October 4, Mack was named NFC Defensive Player of the Month for September. Mack is the first Bears player to win this award since cornerback Charles Tillman in October 2012.
During the Week 6 loss to the Miami Dolphins, Mack suffered a right ankle injury that resulted in him missing the first game of his career two weeks later against the New York Jets. Despite his absence, the Bears limited the Jets to 207 total yards, including just 57 rushing, as Chicago won 24–10. Mack also missed the following week’s 41–9 victory over the Buffalo Bills before returning in Week 10 against the Detroit Lions; in the latter’s 34–22 Bears win, he sacked Matthew Stafford twice.
In Week 11 against the Minnesota Vikings, Mack recorded one sack on quarterback Kirk Cousins and a forced fumble from running back Dalvin Cook in the 25–20 win. Three games later, against the 11–1 Los Angeles Rams, he forced Jared Goff to fumble in a defensive effort that saw the Bears record four turnovers and win 15–6. During Week 15 against the Green Bay Packers, Mack sacked Aaron Rodgers 2.5 times and had two tackles for losses. On his half-sack, Mack was turned around backward by offensive lineman Jason Spriggs; unable to see Rodgers, Mack helped Bilal Nichols bring Rodgers down for a sack by using his back. The Bears won the game 24–17 and won the NFC North while eliminating the Packers from postseason contention.
Mack finished the regular season with 47 tackles, 12.5 sacks, 6 forced fumbles, 2 fumble recoveries, and 1 interception returned for a TD; the 12.5 sacks were the most by a Bears player since Richard Dent in 1993. He was later selected to his fourth Pro Bowl and his third first-team All-Pro, though he did not participate in the former due to injury. He received an overall grade of 90.7 from Pro Football Focus in 2018, which ranked as the 2nd highest grade among all qualifying edge defenders. In June 2019, he received his second career pro Butkus Award.
– Courtesy Wikipedia.org