His career began in the 1930s when he and his older brother Charlie began performing as a duet, the Monroe Brothers. In 1939, after the brothers parted ways, Monroe formed the first edition of the Blue Grass Boys, and the same year became a regular on the Grand Ole Opry.
As a mandolin player, Monroe brought a virtuosity previously unknown in country music to his instrument. In 1945 he hired Earl Scruggs, who similarly elevated the role of the banjo. This version of the Blue Grass Boys, which also included singer/guitarist Lester Flatt, Chubby Wise on fiddle, and Cedric Rainwater on bass, made the first recordings that featured all the elements that later came to be known as bluegrass music.
More than 150 musicians played in the Blue Grass Boys over the years. Many later became stars in their own right, including Mac Wiseman, Sonny Osborne, Jimmy Martin, Don Reno, and Carter Stanley.
Bill Monroe was inducted into the Country Music Hall of Fame in 1971, the IBMA Hall of Honor in 1989, and the Rock and Roll Hall of Fame (as an "early influence") in 1997. He is the only performer honored in all three.