Raised in Illinois, Harmon was educated at Graceland College and the University of Denver following a stint with the U.S. Navy during World War II. He earned a bachelor's degree in radio and began his broadcasting career in 1949 with the Topeka Owls, a minor league baseball team in the Kansas-Oklahoma-Missouri League.
In the 1950s Harmon called play-by-play of numerous sports for the University of Kansas. In 1954, he called baseball for the minor league Kansas City Blues, moving to the major league Kansas City Athletics the following year following that team's relocation from Philadelphia.
In 1961, Harmon went to work for ABC Sports, where he contributed various studio shows and called the baseball Game of the Week (1965) as well as college football for network. In the 1960s, he broadcast for a number of pro football and baseball teams including the Kansas City Chiefs, New York Jets, Milwaukee Braves, and Minnesota Twins.
In 1970, Harmon became lead announcer for the Milwaukee Brewers and continued in that role through the remainder of the decade, teaming with Bob Uecker. He also went into business during this period with Merle Harmon's Fan Fair, a chain of retail stores devoted to licensed sports merchandise.
From 1980-1982, Harmon worked for NBC Sports, calling regional NFL, MLB, and college basketball action and contributing to the weekly Sportsworld anthology series. He was also slated to work on the network's coverage of the 1980 Summer Olympics before the U.S. boycott of those Games.
Harmon worked Texas Rangers telecasts from 1982-1989, then retired from broadcasting.
