Dave was born in Oakland, California, in 1952. There was a half-size violin kept in the closet in case he wanted to be a concert violinist. He played trumpet at the age of nine, moving to baritone horn at the age of eleven, followed by a stint on drums until settling on electric bass at thirteen, adding upright bass to the mix until the switch to saxophone at the age of twenty-one. He has specialized in the baritone saxophone since the early seventies.
Sewelson arrived in New York City in the summer of 1977, settled in the East Village, played in many bands in the area including the 25 O'Clock Band, Jemeel Moondoc’s Jus Grew Orchestra, Noise R Us, Mofungo, Freedomland and Fast 'n Bulbous. He was a founding member of the Microscopic Septet. Lifetime member of William Parker’s Little Huey Creative Music Orchestra.