Thomas Gage, 1st Viscount Gage Bt (bef. 1702 – 21 December 1754) was the son of Joseph Gage of Sherborne Castle and Elizabeth Penruddock.

He married Benedicta Maria Theresa Hall (daughter of Henry Benedict Hall and Frances Fortescue) in 1717. Gage's first son (William Hall Gage, 2nd Viscount Gage) was born in 1718. Gage also had a daughter, Theresa, and a son Thomas Gage who would go on to fame as Commander-in-Chief of the British Army in British America at the beginning of the American Revolution.

On 14 September 1720, King George I created him Baron Gage of Castlebar in the county of Mayo, and Viscount Gage of Castle Island in the county of Kerry of the kingdom of Ireland.

From 1721 to 1754 Gage served in Parliament representing Tewkesbury. As a Member of Parliament he exposed the fraudulent sale of the Derwentwater estates on 31 March 1732, and was subsequently rewarded with £2000 for this under the Greenwich Hospital Act 1735. In 1738, Gage was appointed as Governor of Barbados, but the appointment was never approved, likely because he lacked sufficient political connections.

On 23 April 1744, his cousin, Sir William Gage, 7th Baronet, died without children, and Gage inherited the family manor, Firle Place. Sir William's father was Gage's uncle—Sir John Gage, 4th Baronet, Sheriff of Sussex. Sir William's side of the family had been Roman Catholic recusants who purchased their baronetcy from King James I. Gage however had converted to the Church of England in 1715 for political reasons. He later quietly resumed practising Catholicism, though his children were raised as Anglicans.

His wife died on 25 July 1749, and the Viscount next married Jane Godfrey, a Gloucestershire heiress, on 26 December 1750. Gage had extensive remodelling work done on Firle Place. Between 1743 and 1753 Gage was involved in a number of land rights disputes regarding windfall trees, soil rights, and manorial waste. Gage also spent considerable time collecting paintings which are still housed in the Long Gallery of Firle Place today. From 1747 to 1751 he served as Steward of the Household of Frederick, Prince of Wales. Gage died December 21, 1754, and was buried at Firle.