Sebastian grew up surrounded by music and musicians, including Burl Ives and Woody Guthrie, and hearing such players as Lead Belly and Mississippi John Hurt in his own neighborhood. He graduated from Blair Academy, a private boarding school in Blairstown, New Jersey, in 1962. He next attended New York University for just over a year, but dropped out as he became more interested in musical pursuits.
In the early 1960s, Sebastian developed an interest in blues music and in playing harmonica in a blues style, rather than the classical style used by his father. Through his father's connections, he met and was influenced by blues musicians Sonny Terry and Lightnin' Hopkins (for whom Sebastian served as "unofficial tour guide and valet" when Hopkins was in New York City). Sebastian became part of the folk and blues scene that was developing in Greenwich Village and later gave rise to folk rock.
He played in the Even Dozen Jug Band and in The Mugwumps, which split to form the Lovin' Spoonful and the Mamas & the Papas. Bob Dylan invited him to play bass on his Bringing It All Back Home sessions (though Sebastian's parts probably did not appear on the album) and to join Dylan's new electric touring band, but Sebastian declined in order to concentrate on his own project, The Lovin' Spoonful.
The Lovin' Spoonful
In 1976, Sebastian had an unexpected No. 1 single with "Welcome Back", the theme song to the sitcom Welcome Back, Kotter, causing the label to rush the production of an album, also titled Welcome Back. Despite the "monster hit" status of the song "Welcome Back", Sebastian expressed frustration that Reprise did not do more to promote the associated album, his last for Reprise. His later albums have been released primarily on independent record labels. The song, Sebastian's only top 40 solo hit, found new life 28 years later when a sample from it became the hook for rapper Mase's 2004 hit "Welcome Back".