Harlan began broadcasting as a teenager for his alma mater Our Lady of Premontre High School's high school radio station, WGBP-FM, calling play-by-play for the school's boys' basketball, football and ice hockey teams. He was a ball boy with the Green Bay Packers in his teens during the time that his father, Bob Harlan, was a Packers executive in the front office. He had originally pursued attending either the University of Wisconsin–Madison or the University of Notre Dame in pursuit of his communications/mass media degree, but a personal recommendation from broadcaster Gary Bender to his dad Bob led Kevin to instead attend the University of Kansas and its School of Journalism and Mass Communications. Harlan was introduced to the Jayhawks' primary basketball play-by-play announcer at the time, Tom Hedrick, who audited Harlan's zeal for sports broadcasting and immediately considered him a protege in the making. Hedrick gave Harlan a sideline position, his freshman year, eventually deeming him as his understudy and fill-in announcer on days where he had other commitments. Harlan graduated in 1982 with a broadcast journalism degree.

In 2017, Harlan was voted by his peers as National Sportscaster of the Year by the NSMA. He again was voted National Sportscaster of the Year by the NSMA in 2019. He was also named 2019 National Sportscaster of the Year by The Athletic. In September 2019 Harlan was inducted into the Notre Dame Academy High School Hall of Fame (the former Premontre HS he attended in Green Bay, Wisconsin).