Steward’s family was ‘of Scotch extraction and resided in the early part of the eighteenth century at St. Helena, but subsequently settled at Weymouth’.
In 1778 Steward was returned for Weymouth and Melcombe Regis in place of his wife’s uncle John Tucker who controlled three seats there. That control passed to Steward on Tucker’s death on 9 Oct. 1779, and he also succeeded to Tucker’s lucrative post of paymaster of the marines, which he retained by placing his parliamentary interest at the Treasury’s disposal and by voting regularly with each successive Administration. In 1780 the unexpected dissolution of Parliament found Steward as mayor and returning officer, and therefore ineligible to stand. As a stop-gap he returned Warren Lisle, an aged relation of his wife, who resigned as soon as Steward’s term of office finished. Steward’s election expenses of £500 seem to have been paid by the Treasury.
He could not accuse himself of having ever been guilty of the smallest peculation; but he had much rather have a charge of that kind established against him, than of having ever committed oppression, tyranny, or injustice on any of the natives ... He declared his approbation of a judicature so constituted as that about to take place if the bill passed.
In 1790 Steward sold his property at Weymouth for £30,000 to Sir William (Johnstone) Pulteney, henceforth patron of the borough.
He died 9 Jan. 1792.