Smith’s father was a minor courtier and apparently a client of the 4th Earl of Dorset (Edward Sackville†). He died in late 1634 at Dorset’s seat at Buckhurst, leaving a large family. Smith was the youngest son (his siblings included two half-brothers, and his mother’s two sons by her previous marriage to Thomas Wainwright) and consequently his inheritance was not large. He was, however, able to continue the connexion with the Sackvilles, obtaining a lease of Buckhurst Park through his marriage and eventually becoming steward to the 6th Earl of Dorset and Middlesex (Charles Sackville†).
Smith was a supporter of the Revolution, and in 1689 Dorset, William III’s lord chamberlain, made him knight harbinger. He was returned with Dorset’s support for East Grinstead, not far from Buckhurst, at a by-election in 1693. He was listed as a placeman and Court supporter on Grascome’s list of 1693–5, and appeared on two other lists of placemen in 1693. The presence of John Smith I in the House at this time makes it impossible to attribute any parliamentary activity to Smith with certainty, but it is clear he was not an active Member. He died on 21 Jan. 1695, leaving the bulk of his estate to his surviving brother William.