[2][3] Cathcart was educated at Eton College, an all-boys public school in Berkshire.
Having attended the Mons Officer Cadet School, he was commissioned in the Scots Guards, British Army, as a second lieutenant on 5 August 1972.
[4][2] On 2 March 1975, he was moved to the Regular Army Reserve of Officers, thereby ending his period of active service.
[6] Lord Cathcart was an Associate Member of the Institute of Chartered Accountants.
In April 2019, he opposed an extension to the Article 50 process, stating that "every English and Welsh region outside the M25 would be happy to leave the EU without a deal if no agreement has been reached by the end of next week.