Townshend was the second son of Charles Townshend, 2nd Viscount Townshend, and his first wife the Hon. Elizabeth Pelham. He was educated at Eton in 1718, and was admitted at King's College, Cambridge and Lincoln's Inn in 1720.
Townshend was returned as Whig Member of Parliament for Winchelsea at the 1722 British general election and was appointed under-secretary of state to his father in 1724. At the 1727 British general election, he was returned for both Hastings and Cambridge University and chose to represent Cambridge. He was appointed Teller of the Exchequer in 1727 and held the post for the rest of his life. In 1730 his father went out of office and Townshend lost his position as under-secretary. He was returned unopposed for Cambridge University at the 1734 British general election and was appointed secretary to the Duke of Devonshire, the lord lieutenant of Ireland in 1739. He was returned unopposed in 1741 and 1747.
Townshend married Albinia Selwyn, daughter of John Selwyn, in 1730. Albinia died in 1739. In 1752 Townshend bought Frognal House, near Sidcup in Kent. He survived his wife by over 40 years and died in May 1780, aged 78. Their son Thomas became a prominent politician and was created Viscount Sydney in 1789. Townshend had brothers Charles, William and Roger, and nephews George, Charles and Charles Townshend, 1st Baron Bayning.
- Lee, Sidney, ed. (1899). . Dictionary of National Biography. Vol. 57. London: Smith, Elder & Co.
- "Townshend, Thomas (TWNT720T)". A Cambridge Alumni Database. University of Cambridge.
- "TOWNSHEND, Hon. Thomas (1701-80), of Frognal, Kent". History of Parliament Online (1715-1754). Retrieved 22 February 2019.
- "TOWNSHEND, Hon. Thomas (1701-80), of Frognal, Kent". History of Parliament Online (1754-1790). Retrieved 22 February 2019.