The Bears started the regular season by winning their first three games before losing in weeks four and five to the Detroit Lions and New Orleans Saints, respectively. The following game after winning against the New York Giants, quarterback Jay Cutler suffered a groin injury against the Washington Redskins, as the Bears entered the bye week at 4–3. With Cutler out, Josh McCown stepped in against the Green Bay Packers in week nine, leading the Bears to victory. Cutler returned in the next game against the Lions, but injured his ankle in the loss, and McCown filled in for the next four games; during the four-game span under McCown, the Bears went 2–2, while McCown excelled, throwing thirteen touchdowns and one interception. As a result, when Cutler returned in week fourteen against the Cleveland Browns, controversy arose over who should be the starter. After winning against Cleveland, the Lions lost the following day, allowing the Bears to clinch the NFC North in week sixteen with Packers and Lions losses grouped with a victory over the Philadelphia Eagles. However, the Bears lost 54–11, and in week seventeen against the Packers, the Bears were eliminated from playoff contention with a 33–28 loss.
On December 31, 2012, nine-year head coach Lovie Smith was fired. After Smith's firing, the Bears requested interviews with thirteen coaches, twelve from the NFL and Montreal Alouettes (of the Canadian Football League) head coach Marc Trestman. The hunt later narrowed down to Trestman, Seattle Seahawks offensive coordinator Darrell Bevell and Indianapolis Colts offensive coordinator Bruce Arians. Ultimately, Trestman was hired on January 15.
After Trestman's hiring, he hired New Orleans Saints' offensive line coach Aaron Kromer as offensive coordinator, and the Dallas Cowboys later reported that Joe DeCamillis, who had been among the Bears' 13 head coaching candidates, would join the Bears as the team's assistant head coach/special teams coordinator. Trestman also hired Andy Bischoff and Michael Sinclair as tight ends and defensive line coaches, respectively; both coaches had worked with Trestman in Montreal. Alouettes offensive coordinator Pat Meyer also joined the Bears as offensive line coach, along with Purdue defensive coordinator and colleague of Trestman, Tim Tibesar, as linebackers coach. Former Alouettes coaches Brendan Nugent and Carson Walch were hired as offensive quality control assistants.
On January 15, special teams coordinator Dave Toub announced that he is leaving the Bears for the Kansas City Chiefs. Two days later, it was announced that defensive coordinator Rod Marinelli would not return to the team. Eight assistants were also dismissed: quarterbacks coach Jeremy Bates, running backs coach Tim Spencer, wide receivers coach Darryl Drake, tight ends coach Mike DeBord, offensive line coach Tim Holt, linebackers coach Bob Babich, defensive backs coach Gill Byrd, and offensive coordinator Mike Tice. To replace Bates and Spencer, Chicago hired Matt Cavanaugh and Skip Peete as quarterbacks and running backs coach, respectively. To take Marinelli's place, the Bears hired Jacksonville Jaguars' defensive coordinator Mel Tucker. On February 21, Trestman's staff was completed after the Bears hired Alabama coach Mike Groh as wide receivers coach.
On January 19, Bears director of physical development Rusty Jones announced his retirement after 28 years in the NFL. He was eventually replaced by Mike Clark. On January 28, Chicago hired former Bears safety Chris Harris as defensive quality control, with Sean Desai serving the same position, along with Dwayne Stukes as assistant special teams coordinator.
On May 3, Bears pro scouting director Chris Ballard, who had been hired by general manager Phil Emery, left the team for the Chiefs, and was replaced by assistant director of college scouting Kevin Turks. Regional scout James Kirkland was also let go. On May 6, executive director and Southeastern Conference overseer Ted Monago joined the St. Louis Rams. On the same day, Kevin Turks and Dwayne Joseph were promoted to director of pro personnel and assistant director of pro personnel, respectively; Chiefs area scout Ryan Kessenich was also hired as a scout. Chicago also hired Jay Muraco as scout of the East Coast and Andre Odom as a scouting assistant. The Bears also promoted Breck Ackley to South Central area scout and Sam Summerville to scout the Southeast area and David Williams to player personnel and scout. On May 16, the Bears promoted Southeast area scout Mark Sadowski to senior national scout.