Smith was a moderate
Whig. He was first elected as
Member of Parliament for
Ludgershall at a contest in February 1679, but was defeated in the second election of the year in August. He stood again in 1681, and there was a double return, which was only resolved after the end of that Parliament. In 1689 he was returned unopposed as MP for Ludgershall. Smith was returned as MP for
Bere Alston at a by-election on 15 December 1691. In 1694 he was appointed as a
Lord of the Treasury and became a
Privy Councillor on 23 May 1695. At the 1695 general election he was returned unopposed as MP for
Andover. From 1695 to 1697 he was a Commissioner for Prize Appeals. He was returned unopposed again as MP for Andover at the 1698 general election. On 2 June 1699 he became Chancellor of the Exchequer. He was elected as MP for Andover again at the first general election of 1701, but although he was asked to continue as Chancellor, felt uncomfortable in a changed Parliament and resigned on 27 March 1701. In the second general election of 1701 and in that of 1702 he was re-elected MP for Andover. He was returned unopposed for Andover at the
1705 general election and was chosen as
Speaker of the House of Commons in 1705. In 1706 he was a Commissioner for the Union with Scotland, and was the last
Speaker of the
House of Commons of England. After the
Acts of Union 1707, he became the first
Speaker of the new
House of Commons of Great Britain. He was proposed for this position by his joint partner in the
Company of Scotland,
Francis Montgomerie of Giffen. At the
1708 general election Smith was returned unopposed as MP for Andover, and subsequently gave up his position as Speaker when he was appointed Chancellor of the Exchequer again on 22 April 1708. He ceased to be Chancellor at the dissolution of Parliament on 11 August 1710, and was returned unopposed for Andover at the
1710 election. He was then appointed to the lucrative post of Teller of the Exchequer. He refused to stand for Parliament at the
1713 election, offended by suggestions that the ministry had him under control. His post of Teller was renewed in 1714 and he held it for the rest of his life. Smith was returned as Member of Parliament for
East Looe at the general elections in
1715 and
1722. ==Personal life==