During an eight-season pro playing career, which began in 1948, Keller appeared as a catcher in 25 MLB games for the Washington Senators between 1949 and 1952.

[2] After managing in the Senators' farm system during the late 1950s, he scouted for them until the franchise moved to Minneapolis–Saint Paul as the Minnesota Twins after the 1960 season.

During his two decades as farm and scouting director with the Senators/Rangers and the Mariners, he signed and developed players such as Phil Bradley, Jeff Burroughs, Joe Coleman, Mike Hargrove, Mark Langston, Bill Madlock, Jim Sundberg and Bill Swift.

[1] Keller then served as the Mariners' vice president, baseball operations, and general manager from October 1983 to July 12, 1985, when he resigned.

The Mariners went 115–132 (.466) during his 11⁄2-year term as general manager, while incorporating Langston, Swift, Alvin Davis and Jim Presley into their lineup.