Matthews began developing physically in his senior season, but only garnered interest from Division I FCS schools and local community colleges.

[5] Like his father and uncle, Matthews opted to attend the University of Southern California with hopes of becoming a walk-on for the Trojans football team.

Matthews continued to play reserve linebacker in the 2006 and 2007 seasons, and made two starts in 2007 in place of injured teammate Brian Cushing.

[7] During the off season, Matthews committed to weight training and conditioning programs to gain size and improve his performance level and stamina.

[4] The experiment was successful, as Matthews recorded 4.5 sacks while playing alongside his other NFL-bound teammates Brian Cushing, Rey Maualuga, and Kaluka Maiava.

[9] Matthews, Maualuga and Cushing, were featured on the cover of Sports Illustrated's 2009 NFL Draft Preview magazine, as all three were regarded by it as potential first-round selections.

Analysts were shocked when the Packers traded up for Matthews,[17] whom they did not regard as a first-round draft prospect due to his limited playing experience at USC (only starting the final ten games of his senior season.)

After seeing him double-teamed and constantly chipped by running backs in the NFC wild card game against the Arizona Cardinals, Dom Capers decided to move him around the field.

In the Super Bowl, won by the Packers over the Pittsburgh Steelers, he recorded three tackles, a pass deflection, and a game-changing forced fumble.

He called for teammate Ryan Pickett to "spill it", which meant making Mendenhall redirect his running path further from the center of the line of scrimmage.

The Packers struggled to find pass pressure from the side opposite of Matthews and the loss of defensive end Cullen Jenkins due to free agency and safety Nick Collins due to a career-ending neck injury, placed the Packers last in total defense despite leading the league in interceptions, with 31.

Prior to the 2012 season, Sporting News ranked Matthews as the second-best outside linebacker in the league, only behind Cowboys' star DeMarcus Ware.

After missing four straight games with the hamstring injury, Matthews recorded six tackles, two sacks, and a pass deflection in a 21–13 victory over the Chicago Bears.

[37] Matthews was selected to his fourth straight Pro Bowl, but dropped out due to injury, and was named to the All-Pro team for the second time.

[40] In the off-season, Matthews became the highest-paid linebacker in NFL history when the Packers and he made a deal worth $66 million over the next five seasons.

On November 10, in a game at home against the Philadelphia Eagles, he returned to the playing field, donning a large "club" cast over his entire right hand.

[46] Prior to the 2014 season, the Packers signed veteran free agent Julius Peppers to bring an additional pass rush to help Matthews.

After a Week 8 loss to the New Orleans Saints, where the Packers defense gave up almost 500 yards of offense, including 172 yards rushing from Mark Ingram, Packers defensive coordinator Dom Capers and head coach Mike McCarthy decided to alter Matthews's position, alternating him between outside linebacker and middle linebacker during games, depending on the play call.

[50] Matthews was among the athletes indicated in The Dark Side: Secrets of the Sports Dopers, an Al Jazeera documentary on illegal performance-enhancing drugs use.

[56] On June 2, 2018, Matthews, who was pitching to Packers offensive lineman Lucas Patrick in the off-season Green & Gold Charity Softball Game, had a ball hit directly back to him.

[58] During Week 2 against the Minnesota Vikings, Matthews was called for a controversial roughing the passer penalty that nullified an interception with 1:37 left in the fourth quarter.

[59] During Week 3 against the Washington Redskins, Matthews was again called for roughing the passer, becoming the first player to commit three roughing-the-passer penalties in the first three games of the season since 2001, as the Packers lost 31–17.

[71][72] On November 15, 2023, it was announced Matthews alongside Aaron Kampman would be inducted into the Green Bay Packers Hall of Fame on August 29, 2024.

Matthews had a unique tailgate experience alongside the Crown Royal Rig, a purple 18-wheeler operated by the NFL's official whisky sponsor.

At the stage near the Johnsonville Tailgate Village, Matthews greeted fans, sampled the Canadian Whisky, and made care packages for United States Military service members.

For charity, Matthews agreed to model and test a Depend adult incontinence brief under his uniform during the 2012 season to benefit the Jimmy V Foundation.

Matthews and his wife Casey built a large estate in the Oaks of Calabasas gated community, it went on sale in 2020 with an asking price close to $30,000,000.

[79] Matthews and his former Packers teammates Josh Sitton, David Bakhtiari, T. J. Lang, and Don Barclay had cameo appearances in the film Pitch Perfect 2.

In their aforementioned Calabasas, California estate, an 800-gallon aquarium was installed in his home library, next to his framed uniform worn in Super Bowl XLV.

Main commercial sponsorships for Matthews during his NFL career included: Nike, Gillette, Verizon, Old Spice, Jack Link's Beef Jerky, Campbell Soup Company, Hyundai, Fathead, State Farm (alongside teammates Aaron Rodgers and B. J. Raji) and The Wonderful Company brand pistachios, even with a peanut allergy.