Matthews has broadcast for the Royals since their inception in 1969, when he was the sidekick to Bud Blattner. Blattner retired in 1974, and Matthews has been the Royals' top broadcaster since then. From 1974 to 1998 – a stretch that includes the best seasons in the Royals' history – Matthews was paired with Fred White. In 1999, the two also teamed up to write a book called Play by Play: 25 Years of Royals on Radio, which recounts anecdotes from those seasons. Matthews also called baseball events for the national CBS Radio network in the 1980s.
In 1999, the Royals fired White and replaced him with the younger Ryan Lefebvre. Despite a tremendous age difference, Matthews and Lefebvre integrated their styles well and their dry wit and rapport became popular with Royals fans.
In 2008, Matthews cut back on his broadcast schedule, traveling to fewer road games, turning many of those chores over to Bob Davis and Steve Stewart (who succeeded Lefebvre in the Royals' radio booth while the latter shifted to television). However, Matthews broadcast the first road trip of that season from Detroit and Minnesota while Davis was broadcasting the Kansas Jayhawks' run to the national basketball championship. Matthews handled most of the home schedule and much of the September slate, when Davis turned his attention to broadcasting Jayhawks football games.
Matthews' broadcasts and longevity have made him a popular figure in Kansas City. Baseball historian and statistician Bill James is among his fans, and has written:
His voice has a pleasant timbre which suggests a cheerful occasion. His inflection varies naturally so it's neither falsely enthusiastic nor boring. He has a dry, understated humor that drifts through much of his audience undetected. One cannot learn these things at a microphone; they are given.
Matthews' tenure with the Royals, at 46 years and counting, is the third-longest continuous tenure with one team among current Major League Baseball announcers, trailing only those of Los Angeles Dodgers broadcasters Vin Scully (1950–present) and Jaime Jarrín (1959–present). In January 2015, he signed a contract extension to keep him calling games through his and the team's 50th season in 2018.