He replaced Chip Damiani in the Remains in 1966, shortly before their split.
Smart was a member of Kangaroo, who released one album on MGM Records in 1968. Other members included John Hall (who went on to Orleans), Barbara Keith and Ted Spelies.
He then joined Mountain in 1969 and played on their first gigs, before being replaced by Corky Laing in late 1969. He played with Mountain at Woodstock. The live recording of "Long Red" from the Woodstock set was released on a Mountain live album in 1972. The drum break by Smart has been sampled many times by hip hop artists.