Less than one week after he was fired by the Philadelphia Eagles, McDermott was hired Wednesday to be Rivera's defensive coordinator in Carolina.
McDermott, 36, worked with Rivera for five years in Philadelphia under the late Jim Johnson. McDermott was promoted to defensive coordinator when Johnson died of cancer in 2009.
The Eagles allowed 377 points this season, the most since 1974, leading to McDermott's dismissal Saturday.
It didn't take Rivera long to put McDermott on his first staff. The two sides agreed to a deal earlier this week, with McDermott signing his contract Wednesday.
McDermott replaces Ron Meeks, who recently accepted a demotion to secondary coach.
"I have worked with Sean and know he is an intensely focused and very smart coach," Rivera said. "He has a lot of versatility in his background that provides him with sound experience teaching defense. Sean is a highly regarded young coach, and we think he will make a strong contribution to the Carolina Panthers."
Rivera, who was defensive coordinator in San Diego, said when he was hired this month as John Fox's replacement that he'll run the defense in Carolina. So McDermott might have fewer responsibilities for a unit that started strong but faded this season under the weight of numerous injuries and an NFL-worst offense that put the defense in tough spots.
Rivera said the Panthers will continue to use a 4-3 scheme based on their personnel -- and might take a premier defensive player with the No. 1 overall pick in the draft.
McDermott, a former defensive back at William & Mary, joined the Eagles as a scouting administrative coordinator in 1998. He was promoted to assistant coach one year later and worked with both defensive backs and linebackers.
In McDermott's first season as defensive coordinator in 2009, the Eagles forced 38 turnovers and had 44 sacks, each of which ranked third in the NFL. They forced 34 turnovers this season but struggled to keep teams out of the end zone, and McDermott was let go despite Philadelphia reaching the playoffs.
The Associated Press contributed to this report.