When Reid departed Philly for the Kansas City Chiefs, he took Nagy with him and made him his quarterbacks coach. After three seasons in that role he was promoted to offensive co-ordinator — and that's when he really started to shine.
After a run of five defeats in six games midway through the 2017 season, Reid ceded playcalling duties to Nagy and the Chiefs responded by winning four of their remaining five games to make the playoffs.
The Chicago Bears took note while searching for their new head coach and signed Nagy to a position which on average pays around $7 million a year.
Sports Illustrated's Peter King described the gamble Nagy took to pursue an NFL coaching career as "either the most inspirational story about living your dream, or is so far-fetched that any thinking person would say, 'This story is true, but it's such a fairy tale you can't realistically expect it ever to happen to you. Dream, but dream realistically'."
The Bears were looking for a coach to get the most out of quarterback Mitchell Trubisky and help a founding NFL franchise emerge from one of its worst runs. They believe Nagy is the right man.
The Bears announced the move a week after firing coach John Fox, who went 14-34 in three seasons for a .292 winning percentage that is the second-lowest in team history. Chicago was 5-11 this season and hasn't finished above .500 since letting Lovie Smith go following a 10-6 finish in 2012, two years after its most recent visit to the playoffs.
The 39-year-old Nagy spent 10 seasons working under Andy Reid in Philadelphia and Kansas City and drew praise for his work with Chiefs quarterback Alex Smith.
In Chicago, the former quarterback at Delaware and then the Arena Football League will be trying to develop Trubisky, last year's No. 2 overall draft pick.
"He's a good football coach, first of all," Reid said. "I appreciate the way he comes to work and the attitude he brings. He puts his own flare on things. I think that's important to know. Everybody does it their way."
The Bears were 3-15 against the NFC North under Fox and dropped all six division games this past season. That will be one of the many things Nagy will need to help solve.
"Up-and-coming, smart guy," Chiefs assistant head coach Brad Childress said of Nagy. "He's played the quarterback position, so he gets it. He knows how to teach. He's got a great demeanour about him. He's got a creative mind. I think he's got everything going for him."
- With AP.