He was a keen amateur geologist, with enough recognition to warrant being made a Fellow of the Royal Society of Edinburgh.

[2] Cathcart entered the army as a cornet in the 2nd Regiment of Life Guards on 2 March 1800.

Cathcart saw service on the ill-fated Walcheren Expedition in 1809 and at the siege of Flushing, after which for some time he was disabled by the injurious effects of the pestilence which cut off so many thousands of his companions.

[3] He was next sent to assist Sir Thomas Graham in Holland as the head of the quartermaster-general's staff and was present at the ill-fated Siege of Bergen op Zoom in March 1814.

[5] He became involved in the proceedings of the Highland Society, became a Fellow of the Royal Society of Edinburgh and where he announced the discovery of a new mineral, a sulphide of cadmium, which was found in excavating the Bishopton tunnel near Port Glasgow and which is now known as Greenockite.