In 1771 he went to
St. Petersburg, where his father,
Charles Cathcart, 9th Lord Cathcart, a general in the army, was ambassador. He became an excellent horseman in Russia then from 1773 to 1777 he studied
law at the
University of Glasgow and was afterwards called to the
Scottish Bar. He succeeded to the lordship upon his father's death in 1776, and inherited several properties including Schawpark an estate near
Sauchie where his father had commissioned
Robert Adam to remodel the mansion house but the works were incomplete when his father died. In 1777 he obtained a commission in the
7th Dragoons. He was elected a
Scottish representative peer in 1788, and in 1792 he became colonel of the
29th Foot. He served with distinction in the campaigns in the
Low Countries, 1793–1795, in the course of which he was promoted major general; and in 1801 he was made a lieutenant general, having in the meanwhile received the appointments of
Vice Admiral of Scotland (1795),
privy councillor (1798), and colonel of the 2nd Life Guards (1797). From 1803 to 1805 Lord Cathcart was Commander-in-Chief in Ireland, and in the latter year he was sent by
Pitt to supersede
Sir George Don in command of the 14,000 strong British
Hanover Expedition. He occupied Hanover on 14 December and joined with Werdereffsky's Russian column of
Tolstoi's corps. After skirmishes with the French forces of
Gabriel Barbou des Courières at
Springe, Cathcart was forced to withdraw after the Franco-Prussian agreement of 27 January 1806 handing over Hanover to Prussia, and re-embarked for the United Kingdom on 7 February 1806. After the recall of this expedition Cathcart
commanded the forces in Scotland until 1807, when he was placed in charge of the
expedition to Copenhagen, which surrendered to him on 6 September. Four weeks later he was created Viscount Cathcart of Cathcart and Baron Greenock of Greenock in the
peerage of the United Kingdom, resuming the Scottish command on his return from the front. On 1 January 1812 he was promoted to the full rank of general, and a few months later he proceeded to
Russia as ambassador and military commissioner. In the latter capacity he served with the headquarters of the allies throughout the
War of Liberation (1812–1814); his success in the delicate and difficult task of maintaining harmony and devotion to the common cause amongst the generals of many nationalities was recognized after the war by his elevation to an earldom (July 1814). He then went to
St. Petersburg, and continued to hold the post of ambassador. During this time, Cathcart participated in the
Congress of Vienna. He held the role of ambassador until 1820, when he returned to his home in Britain. He died at his estate near
Glasgow on 16 June 1843. He is buried in
Paisley Abbey with a monument by
William Mossman erected in 1848. ==Family==