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John Harbaugh learned a lot from Andy Reid in their 10 years together on the Eagles’ coaching staff. Not everything that worked in Philadelphia also worked in Baltimore. But a lot of it did. Some stuff even ended up working out better.

Harbaugh’s 18-year run as the Ravens’ head coach, which ended with his surprise firing Jan. 6, was among the more successful tenures of any NFL coach in the 21st century, surpassing even Reid’s in Philadelphia. Harbaugh won a Super Bowl; Reid lost in his lone trip. Harbaugh posted a .614 winning percentage; Reid finished at .583 over 14 Eagles seasons. Harbaugh won six division titles; so did Reid.

Now, with the New York Giants having hired Harbaugh as their fifth full-time head coach of the past decade, the 63-year-old will soon start a second act that will be celebrated in East Rutherford, New Jersey, and closely watched in Owings Mills. Will Harbaugh flower as the 67-year-old Reid has in Kansas City, where, along with Patrick Mahomes, he’s won three Super Bowl titles and transformed the Chiefs into a perennial power?

Or will he flounder as former Seattle Seahawks coach Pete Carroll did in Las Vegas, where the 74-year-old was fired as Raiders coach after a miserable debut year?

At his news conference Tuesday, Ravens owner Steve Bisciotti acknowledged the difficulty in moving on from Harbaugh just four months after the team had opened the season as Super Bowl favorites. “I know that this is the hardest thing that we’ve ever had to do,” Bisciotti said. “I don’t think any one of you think we blame John, completely, for our falling off our quest for Super Bowls.”

Harbaugh inherits no such expectations as Giants coach. But comparisons to his mentor will be unavoidable. Reid needed just one season to take a two-win Chiefs team back to the playoffs. He needed just four seasons to win the AFC West. He needed just seven seasons to lift the Lombardi Trophy for the first time.

In Jaxson Dart, Harbaugh will have at least one of the ingredients that supercharged his two turnarounds in Baltimore and Reid’s mini dynasty in Kansas City: a promising quarterback on a team-friendly rookie contract.

Over Joe Flacco and Harbaugh’s first five years in Baltimore, the Ravens went to the playoffs five times, advanced to three AFC championship games and won Super Bowl XLVII. Over Lamar Jackson’s first five years in Baltimore, the Ravens went to the playoffs every year that he finished the season healthy and advanced to the divisional round twice.

But, even if Dart can be the force multiplier Harbaugh covets at quarterback — a big if, considering the rookie’s reckless playing style and concussion history — the Giants’ to-do list is longer than any left to Harbaugh over his final years in Baltimore.

The top-line items are different. On offense, wideout Malik Nabers should solve the WR1 problem that Harbaugh had for years in Baltimore. On defense, Harbaugh should have the star power to support a pass rush — Brian Burns, Dexter Lawrence, Abdul Carter — even when his scheme cannot.

But everything else about the Giants’ rebuild will test Harbaugh’s skills in identifying and nurturing talent, and in fostering a winning culture. Can he rebuild a coaching staff and locker room free of the drama that plagued the end of former Giants coach Brian Daboll’s tenure? Harbaugh took pains to shield his staffers and players from slings and arrows, but his occasional public scolds — not to mention the criticism aimed at him — would be magnified in the New York media market.

Can Harbaugh find the right assistant coaches to develop a promising offensive line? In Baltimore, several Ravens starters stagnated or regressed in their second years under offensive line coach George Warhop.

Can Harbaugh lead a quick fix of a chronically underperforming defense? The Ravens’ schemes in his tenure were among the NFL’s most influential, but he cycled through assistant coaches on defense in recent years, and few veterans leveled up under coordinator Zach Orr this past season.

Can Harbaugh reinvigorate the Giants’ special teams? His experience as the Eagles’ special teams coordinator imported a standard of excellence to Baltimore, but the Ravens finished only 23rd and 12th there in overall efficiency over the past two years, according to FTN, rare seasons outside the top 10.

And, maybe most important, can Harbaugh transcend a questionable front office — or perhaps even lead one himself?

Giants general manager Joe Schoen has tenuous job security after a series of high-profile blunders that have alienated the fan base. Harbaugh arrives with considerable sway in roster decisions. If Schoen is fired, Harbaugh could fill the void as the Giants’ de facto personnel chief.

In Baltimore, he had the benefit of one of the NFL’s best security blankets: a front office led by GM Eric DeCosta that strives to optimize its draft process, retain homegrown talent and keep the team’s window for contention open as long as possible.

It could take leaving Baltimore for Harbaugh to appreciate what he had with the Ravens. The grass was not greener elsewhere for Carroll, who stepped down in Seattle two years ago after 14 seasons as the Seahawks’ head coach. His reputation as a culture setter and floor raiser went unrealized in Las Vegas.

Rampant dysfunction under first-year offensive coordinator Chip Kelly and an apparent disconnect between the coaching staff and front office reportedly undercut the Raiders as they finished 3-14, their fewest wins in over a decade.

It could also take leaving Baltimore for Harbaugh to break out of the coaching rut that doomed his Ravens tenure. Among Harbaugh’s greatest virtues as a coach is his curiosity; through his work with the Harbaugh Coaching Academy, he’s interviewed a handful of fellow head coaches, even Kevin Stefanski, then leading the rival Cleveland Browns, probing them for ideas and insights.

Over a disappointing 2025, Harbaugh rarely seemed to find the right message for his own Ravens team. If he fails with the Giants, it won’t be for lack of trying. Harbaugh’s openness to evolution and compromise made him the longest-serving head coach in Baltimore’s professional sports history. Now comes the biggest change, and challenge, of his career.

“Coaching at any level is a day-to-day job, and your job is to do the best job you can today, and to do everything you can to help your players and your coaches — if you’re a head coach — be the best they can be every single day,” Harbaugh said late in the season, as questions swirled about his job security.

“We have responsibilities, and we’re given opportunities to steward those responsibilities, and you’re given a job to do that until you’re not. And then I try to do the job, not try to keep the job, because there’s no such thing as having a job. You’re just doing a job.

“And so my focus is on always ... to try to do the best job I can today and fight as hard as I can so the guys have the best chance to be successful today. And, anything after today, I’m not thinking about, because it’s not given for us to think about. We don’t have control over that, except for the job we do today. And if we do a good enough job today, then the opportunity to do that job or a different job will be there tomorrow, and that’s what you hope for.”