On Friday, Schefter reported the two sides agreed on a four-year contract.
Gregg Rosenthal of NFL.com summed up Lynn's fast rise:
Lynn spent the last two seasons with the Buffalo Bills as offensive coordinator and running backs coach before briefly serving as interim head coach.
The 48-year-old Texas Tech product guided Buffalo's rushing attack to the top of the league. The LeSean McCoy-led group averaged 164.4 yards per game and, perhaps even more impressively, a terrific mark of 5.3 yards per carry.
Lynn spent six seasons in NFL backfields between two stints with the Denver Broncos and one with the San Francisco 49ers. His first coaching job also came with the Broncos as a special teams assistant in 2000.
While the two-time Super Bowl champion had a plan in mind after taking over as the Bills offensive coordinator in September, he explained his feedback-orientated approach when he accepted the biggest coaching role of his career to Chris Brown of the Bills' official website:
I met with the players and I told them we were going to salvage the season. I told them how I was going to operate and what I expected from them. And that I was open to feedback because I was going to put it on them.
You're not worth a crap until the players take ownership of it and go out and do it. They agreed to do that. Some guys gave me some feedback. I took it into consideration and I said, 'Okay, let's go with it.'
Now he'll be tasked with building that trust and openness across a 53-man roster.
It's the first time Lynn has held a head coaching job, aside from a one-game stint in an interim position for the Bills after Rex Ryan was fired. That said, he's worked under several notable coaches during his career, including Bill Parcells, Mike Shanahan, Jack Del Rio and Romeo Crennel.
Lynn and the Chargers are a nice fit on paper. He benefits from having a franchise quarterback on the roster in Philip Rivers, a rare luxury, and the team's 26th-ranked rushing attack should get a boost from his arrival, especially with Melvin Gordon in his prime.
The key question now surrounds the defensive staff he'll build. The defense ranked 16th in yards allowed and 29th in points allowed this past season. The latter figure must move closer to the middle of the pack, at a minimum, in order to contend for the playoffs.
The Chargers also blew a number of close games in 2016, leading to their disappointing 5-11 record under former head coach Mike McCoy.
Albert Breer of The MMQB broke down some possibilities for the staff:
Lynn earned this opportunity, but the pressure will be intense in a new city. Rivers, 35, only has a few good years left too.