As a teenager, he moved to North Carolina to work in a silk mill. While there, he married his wife, Gladys, with whom he began performing as a duo. When the mill shut down, the Flatts returned to Tennessee for a short time before moving to Virginia. As the result of a bout with rheumatoid arthritis, Flatt quit the mill permanently to focus on a career in music.
He palyed with a handful of groups before being invited by Charlie Monroe to join the Kentucky Pardners in North Carolina. Charlie had Flatt playing mandolin and singing tenor, niether of which pleased Flatt too much. Upon finally leaving the Kentucky Pardners, Charlie's brother Bill Monroe immediately invited Flatt to join his Blue Grass Boys as a guitar player and lead singer. His first gig with the band was in 1945 at the Grand Ole Opry, with no prior rehearsal.
Soon after, banjo player Earl Scruggs joined the Boys, as well, and the group surged to popularity, holding down a rigorous tour schedule for nearly three years. Tired of the road, Scruggs left the band in 1948, followed soon after by Flatt and Cedric Rainwater.
Together, the three formed Flatt & Scruggs' Foggy Mountain Boys, who became one of the most influential bands in the genre. Flatt and Scruggs continued to perform together until 1969, when they went their separate ways. Lester formed the Nashville Grass, with whom he played for ten years before his death on May 11, 1979.
