On Monday, Dallas Cowboys owner and general manager Jerry Jones picked McCarthy to be the ninth coach in franchise history, according to a source, and AT&T Stadium will be McCarthy's new home.
Of the other coaches available, none had a résumé like McCarthy.
He posted a 125-77-1 record in 13 seasons with the Packers and went to the playoffs nine times. He won one Super Bowl and made two more NFC Championship Games. He also ended the Cowboys' season twice in the divisional round of the playoffs (2014 and 2016).
He is one of four NFL coaches to lead a single franchise to at least eight straight playoff appearances, along with Tom Landry, Chuck Noll and Bill Belichick. He won more games with the Packers than anybody but Curly Lambeau.
Things did not end well for him in Green Bay, and no coach has won a Super Bowl with two different teams, but the Cowboys are banking on McCarthy being the guy to take them to places former coach Jason Garrett couldn't.
With McCarthy on board, let's break down what it all means.
What did McCarthy learn from his time in Green Bay?
Clearly, he convinced the Cowboys he has learned some hard lessons. Things grew stale near the end in Green Bay with the Packers missing the playoffs in 2017. He was subsequently fired on Dec. 2, 2018 with four games to play and a 4-7-1 record.
Some will look at a résumé with one Super Bowl win with quarterback Aaron Rodgers as a disappointment. But, have Sean Payton and Drew Brees been a disappointment in New Orleans with one Super Bowl win?
Taking the past year off and away from the NFL likely freshened McCarthy in a number of ways, including his approach.
If there is a comparison the Cowboys would like to make between McCarthy and another coach whose long run in one spot grew stale, it's Andy Reid in Philadelphia.
The Eagles went to the playoffs in nine of Reid's 14 seasons, including a Super Bowl appearance, but it ended poorly with a 4-12 record in 2012.
Reid was immediately hired by Kansas City in 2013 and has not had a losing record in seven seasons with the Chiefs. While he has not been to a Super Bowl yet, Reid has adapted and adjusted to one of the most-potent offenses in the NFL with Patrick Mahomes at quarterback.
Also, Reid was 55 when he took over in Kansas City. McCarthy is 56.
What happens to the current Cowboys' offensive coaches, such as Kellen Moore?
In his first year as the coordinator, the Cowboys had the No. 1 offense in terms of yards per game and sixth in points per game. With 4,902 passing yards, quarterback Dak Prescott finished 2 yards shy of setting the team's single-season record for passing yards. Running back Ezekiel Elliott (1,357) ran for more than 1,000 yards, and Amari Cooper (1,189) and Michael Gallup (1,107) each had more than 1,000 receiving yards.
It wasn't all perfect for Moore, but there is something to work with in 2020. The same goes for offensive line coach Marc Colombo. Prescott went from being sacked 56 times in 2018 to 23 times in 2019. Tyron Smith, Travis Frederick and Zack Martin were named to the Pro Bowl. Right tackle La'el Collins had his best season. Quarterback coach Jon Kitna also seemed to get the best out of Prescott.
There is a lot to like about the Cowboys' personnel and assistants, but the answer is up in the air as of now because there's uncertainty if McCarthy will want to bring in his own coaches.
McCarthy was the Packers' offensive playcaller until making the decision in 2014 to give up the duty because he felt he needed to spend more time on defense and special teams. But, during the 2015 season and against the Cowboys on Dec. 13, in fact, McCarthy resumed calling the team's offensive plays "because I feel as the leader of this football team I've got to make sure to maximize all the opportunities and resources to [save] and to give our team the chance to win."
During his time away from the NFL, McCarthy spent time doing extensive and high-tech studies on his coaching experiences as well as historical references on what happened week to week around the NFL. He built a warehouse of information and film, including: a blueprint for a coaching staff, a refurbished playbook and new practice schedules, and put together ideas for a heavily staffed team of analytics and football technology departments.
And, moving on to the defensive side of the ball ...
Unlike the offense, most of the current Cowboys' defensive coaches are on contracts that are about to expire or have expired, including coordinator Rod Marinelli and passing game coordinator Kris Richard. There is no way to sugarcoat it -- the defense underperformed in 2019, allowing 327.0 yards per game.
New Orleans Saints linebackers coach Mike Nolan will be the Cowboys' defensive coordinator under McCarthy, a source told ESPN. Nolan hired McCarthy as offensive coordinator in San Francisco in 2005.
McCarthy employed both 4-3 and 3-4 schemes during his time in Green Bay. The Cowboys are not built for a switch to the 3-4, but they could be ready for a move from the Seattle-type 4-3 they have used since 2014. Richard has interviewed for the New York Giants' coaching vacancy and could be an option for other franchises. The sense around the team has been that the Cowboys are ready to move on to someone else to control the defense in 2020.
Ryan: McCarthy is not a sexy hire for Cowboys
Rex Ryan says Mike McCarthy is going into a great situation in Dallas, but he doesn't believe McCarthy is the long-term solution at head coach for the Cowboys.
What do the changes mean for Prescott?
Instead of remembering how things appeared to end between McCarthy and Rodgers in Green Bay, choose to look at the successes they had together.
Prescott made strides as a passer in 2019 with career highs in touchdown passes (30) and yards.
"Dak-friendly," has been a term used around the Cowboys the past few years. It's hard to see how this union with McCarthy won't be a "Dak-friendly," situation. Prescott played out his rookie contract, but he will not hit the open market. He is, however, looking at a huge raise, either with the franchise tag, which could run anywhere from $27 million to $33 million in 2020, or a multi-year deal that could guarantee him more than $100 million.
Would McCarthy simply throw out all of the good things the Cowboys have done with Prescott for the sake of running his own system? You would have to think that was a huge part of the interview process.