Harlan's broadcasting career began in 1982, when he became the TV and radio voice of the NBA's Kansas City Kings (now the Sacramento Kings). He then was a basketball announcer for his alma mater, the University of Kansas, for one year, then went on to call games for the NFL's Kansas City Chiefs from 1985–93. Harlan also split time with the University of Missouri (1986–89) calling football and basketball games, and worked as the play-by-play voice of the NBA's Minnesota Timberwolves for nine seasons (1989–98). On the network level, Harlan called NFL football for NBC in 1991, college football for ESPN in 1992–93, NFL for Fox from 1994–97, and joined Turner Sports in 1996 to cover NBA playoff games (he would begin calling games throughout the entire season in 1997, which he continues to do to this day). He began working for CBS in 1998.
In addition, Harlan has called Jacksonville Jaguars, Chicago Bears and Green Bay Packers preseason games; basketball games during the now-defunct Goodwill Games, which were owned by Time Warner; college sports on ESPN; and several bowl games during college football seasons. A Wisconsin native, Harlan attended the University of Kansas and graduated in 1982 with a broadcast journalism degree. He took sportscasting classes under the guidance of former Super Bowl and Chiefs play-by-play voice Tom Hedrick.
He has also lent his voice on the NBA 2K video game series. Curiously, his voice is similar to fellow NBA on TNT announcer Marv Albert that 2K Sports turned to him as a play-by-play announcer for said video game, in response to Albert being the voice on competitor EA Sports' NBA Live series.
Harlan's creative banter includes lines such as: "Buckle up for..." (when any NBA player is about to slam dunk the ball), "Right between the eyes!", "He just sucked the gravity right out of the building!", "He's a flamethrower!", "He is an assassin", "Flight (jersey number) is cleared for landing!", "Up high...and down hard! (followed by the player's first and last name)", and "Good!". Harlan has also been known to exclaim "(Kobe Bryant/LeBron James), with no regard for human life!" after an especially devastating play. The most well known are a dunk by Kobe Bryant against the New York Knicks in 2003 and the LeBron James dunk on Kevin Garnett in the 2008 Eastern Conference Semifinals. "LeBron James, with no regard for human life!"
In a 2003 playoff game between the Los Angeles Lakers and Minnesota Timberwolves, Kobe Bryant performed a reverse windmill dunk over several defenders to which Harlan responded, "Buckle up for Kobe Bryant! Kobe Bryant just sucked the gravity out of the Target Center!" During a playoff game in 2005 between the Houston Rockets and the Dallas Mavericks, the Rockets' Tracy McGrady drove to the rim and threw down a vicious one handed facial on the Mavericks' Shawn Bradley, and Kevin Harlan said, "Here comes McGrady--OH, he just sucked the gravity right out of the building! What a play by T-Mac!" Although this line is most commonly associated with McGrady's dunk, Harlan actually used the same line for a Keon Clark dunk in a 2002 Raptors-Mavericks game. Coincidentally, the Keon Clark dunk was also on Shawn Bradley.
On April 20, 2011 in a first round playoff game between the Los Angeles Lakers and the New Orleans Hornets, former guard of the Hornets Chris Paul, had made two buzzer beater three-point shots, one in the second quarter and the other in the third quarter. When the third quarter buzzer beater was made, Harlan had said, "Paul, with a three! Good! Right between the eyes!"
Leading up to the start of the 2012–13 NBA season, his call of Derrick Rose's knee injury from the previous playoffs, "Holding onto his knee. Holding onto his knee and down", was used in Rose's adidas sneaker commercial.
In the second round of the 2013 NCAA Tournament, Harlan exclaimed "Ooooh! He drops the anvil!" when Chase Fieler made an alley-oop slam against the Georgetown Hoyas in FGCU's upset win.