Twice guitarist for Captain Beefheart, St. Clair was a contemporary of Frank Zappa at high school in California, where St. Clair played trumpet and Zappa played drums. They bought their first guitars within days of each other. St. Clair joined his first band, The Omens, around 1959.

In 1965, he teamed up with Doug Moon, Jerry Handley and Terry Wimberley in a blues band. After Van Vliet was invited to sing with them and Vic Mortenson had been picked as drummer, the first incarnation of the Magic Band was formed. It was around this time that Snouffer changed his name to St. Clair and Vliet became Captain Beefheart.

St. Clair played on the band's first two albums, Safe as Milk (1967) and Strictly Personal (1968), before becoming both musically and financially disappointed after a botched European tour. Bill Harkleroad eventually took his place in the band.

St. Clair returned to music in Denny King's Boogie Band and appears on their album Evil Wind Blowing. Surprisingly, he rejoined the Magic Band after the departure of Elliot Ingber, and was with them for the Clear Spot tour of North America and Europe. St. Clair again left the band due to financial problems, as did Harkleroad, Mark Boston and Art Tripp.

St. Clair was found dead in his apartment at the beginning of 2006.