Cary is the eldest of four children, and the only son of Lucius Cary, 14th Viscount of Falkland, and Constance Mary Berry, daughter of Captain Edward Berry.

Cary was educated at Wellington College in Berkshire, and was formerly an officer in the Hussars.

Following the removal of the majority of hereditary peers under the House of Lords Act 1999, he was one of the ninety-two elected to remain.

In 2011 Falkland left the Liberal Democrats and sat as a Crossbencher until his retirement in 2023.

[1] He is a supporter of Humanists UK,[citation needed] and has been a vice-president of the Royal Stuart Society since 2015 (his ancestors were ardent Jacobites, and he holds the title of 10th Earl of Falkland in the Jacobite Peerage).