A Massachusetts native, Keith was born in Boston in December 1939 and graduated from Amherst College in 1961. During his youth, he played with a few Dixieland bands before acquiring an interest in folk music through listening to Pete Seeger and Earl Scruggs, among others. Inspired by them and eager to play fiddle tunes on the banjo, he began developing his own picking style. He and fellow Amherst student Jim Rooney teamed up in the late 1950s to play on campus and at local coffeehouses and also partnered in launching the Connecticut Folklore Society. Keith was a member of Bill Monroe’s Bluegrass Boys for a short while in the early 1960s. During that brief stint of recording and performing, Keith left an indelible mark on banjo playing, while his melodic style – a variation on the then-popular “Scruggs style” that would later become known as “Keith style” – has influenced many banjoists.
Shortly after leaving the Bluegrass boys, Keith joined and spent four years with the Jim Kweskin Jug Band. He later played with Ian and Sylvia before moving to Woodstock, New York in 1970 and playing with Jonathan Edwards for a year. During the 1970s, he recorded for Rounder Records and also played with Judy Collins and was part of the Woodstock Mountain Revue. In the years since then, he also performed with Muleskinner (featuring David Grisman, Peter Rowan and Clarence White) and Tony Trischka, among others.
Keith also is credited with designing a specialized type of banjo tuning peg — now known as Keith Pegs — that enables players to change quickly from one open tuning to another. His invention – which he continued to market and manufacture through his Beacon Banjo Company (now run by his son, Martin) until his death –was an improvement over a previous design by Earl Scruggs.