He was born to Henry Charles Gage and Leila Georgina Peel. His Gage family ancestry included extensive roots in British North America from the Schuyler family, the Delancey family, and the Van Cortlandt family.
Upon the death of his father in 1912, he succeeded him as Viscount Gage when he was only 16. Gage served in World War I as a Captain of the Coldstream Guards, seeing action in both France and Belgium. He was appointed Honorary Colonel of the 58th (Home Counties) Field Brigade, Royal Artillery, on 17 June 1936.
In 1931, Gage donated papers and letters written between 1758 and 1764 by his famous relative General Sir Thomas Gage to the William L. Clements Library of Ann Arbor, Michigan. Gage later (between 1958 and 1965) donated letters and documents from ancestral in-law Vice-Admiral Sir Peter Warren to the Sussex Archaeological Society in Lewes.
At the beginning of World War II the family moved to a smaller house and nearby Southover girls' school in Lewes was evacuated for a short time to Gage's family home in Firle. After they had moved, Canadian soldiers were quartered at the family manor. In 1952, Gage's mother-in-law died, leaving art work to his wife, Imogen. The couple decided to showcase the art in their home, opening Firle Place to public tours in 1954.
In 1968, Imogen died. Gage was remarried in 1971 to Diana Cavendish. He died himself in 1982 at the age of 86. A stained glass window by the artist John Piper was installed in St Peter's Church, Firle, and dedicated to his memory.
He was appointed Deputy President of Sussex Wildlife Trust on 13 January 1962 and retired at the AGM on 29 April 1967. He is listed as the Director of Over Timber (Fawley) Ltd. and of Firle Estate Co.Ltd
On 26 February 1931, Gage married Alexandra Imogen Clair Grenfell (Imogen), daughter of William Grenfell, 1st Baron Desborough; they had three children:
In 1932 John St Clere (whom they called "Sammy") was born. George John would go on to become the 7th Viscount Gage. The future 8th Viscount Gage (Nicolas Gage) was born to Lord and Lady Gage in 1934. They also had a daughter, Camilla Jane, in 1937.