Harbaugh attended college and played varsity football as a defensive back at Miami University, where he graduated in 1984.

[5][6] Harbaugh worked as an assistant at Western Michigan (1984–1986), Pitt (1987), Morehead State (1988), Cincinnati (1989–1996), and Indiana (1997).

[1][17] He was not considered one of the favorites for the position because he had no head coaching experience at any level and had never been an offensive or defensive coordinator in the NFL.

[18] He impressed team owner Steve Bisciotti and Vice President of Player Personnel/General Manager Ozzie Newsome.

New England Patriots head coach Bill Belichick also recommended Harbaugh to Bisciotti by phone during the interview process.

[22] In the playoffs, he led the team to victories over the Miami Dolphins and Tennessee Titans before losing to the Pittsburgh Steelers in the AFC Championship Game.

[23][24][25] On January 26, 2009, he named Greg Mattison the defensive coordinator for the Ravens, replacing Rex Ryan who had left to take his first head coaching job (with the New York Jets).

In his second season as Ravens' head coach, he once again led the team to the playoffs with a 9–7 record during the regular season and improved his playoff record to 3–1 with an upset 33–14 victory over the New England Patriots in the AFC Wild Card Round on January 10, 2010, before losing in the AFC Divisional Round 20–3 to the Indianapolis Colts.

[34] The Ravens finished the 2011 season with a 12–4 record, winning the AFC North and sweeping the Pittsburgh Steelers home and away.

[36] The Ravens lost the AFC Championship to the New England Patriots after Lee Evans had a potential late game-winning pass knocked out of his hands by Patriots defensive back Sterling Moore and kicker Billy Cundiff missed a potential game-tying field goal.

[39][40] They again met the New England Patriots in the AFC Championship (on January 20, 2013), got their revenge with a 28–13 victory (coming from behind with a 13–7 second half), and was the first time Tom Brady and Bill Belichick lost a home game after leading at halftime, giving John the opportunity to face brother Jim and the San Francisco 49ers in Super Bowl XLVII on February 3, 2013.

[45] On September 5, 2013, an hour before the Ravens played in the NFL regular season's opening game, it was reported that Harbaugh had signed a four-year contract extension in a deal that was reached "months ago.

[48][49] In each of Harbaugh's first four seasons and again in 2014, every AFC Champion defeated the Ravens in the playoffs (although only the 2008 Pittsburgh Steelers and 2014 New England Patriots were able to actually win the Super Bowl).

[53] After the game, Harbaugh complained about the Patriots' uncommon but legal tactics of declaring receivers eligible and ineligible, saying "It was clearly deception.

[55] The Ravens lost many close games and key players like Joe Flacco, Justin Forsett, Steve Smith Sr., Eugene Monroe, and Terrell Suggs all suffered season-ending injuries.

[74][75] Harbaugh came under scrutiny where he called a two-point conversion late in the fourth quarter twice to put the Ravens up by one, which both failed.

[77] December 11, 2022, marked the 32nd matchup between Harbaugh and Pittsburgh Steelers head coach Mike Tomlin, surpassing Curly Lambeau and Steve Owen for the second-most head-to-head matchups between head coaches in NFL history (the current record is held by Lambeau and George Halas with 49).

[91] John was roommates with the late Brian Pillman of WCW, ECW, and WWE fame while in college at Miami University in Ohio.