Born in the colony of New York, Morris parlayed a marriage to a Scottish noblewoman into a successful career as a military officer and politician in the British Parliament.

After serving in India from 1762 to 1763 during the Seven Years' War, Morris focused his attentions on American affairs, receiving 10,000 acres (4,000 ha) of land grants in Canada.

[5][6] As noted by British historians Lewis Namier and John Brooke, the Duchess had been searching for an eligible bachelor "for some time.

"[7] At the time of their marriage, Morris was only at the rank of captain in the British Army and ten years her junior, which according to English historian Stephen Conway "raised [eyebrows] in polite society".

[9] In 1759, the Duchess persuaded King George II to allow Morris to raise a Highland regiment in the traditional territories of the Clan Gordon, a region she was familiar with.

[8] Morris himself did not leave England until April 1762, when he finally travelled to India and joined his regiment, which was stationed in the Bombay Presidency.

Returning to Scotland in 1769, his friendship with the 4th Duke of Gordon helped Morris to be elected to the House of Commons, representing Elgin Burghs from 1774 to 1784.

"[3][13] Morris was promoted to the rank of major-general in 1777, and made an application to command the 50th Regiment of Foot, which was unsuccessful despite being supported by incumbent Prime Minister Lord North.

Upon Sarah Gouvernour's death in 1786, Morris inherited her family estate, which had been partially damaged by British forces during the American Revolution.

[18] Morris was born into a prominent Anglo-American colonial family whose members had long been influential in the English colonization of both New York and New Jersey.

[3] Though his marriage to the Duchess initially proved to be controversial among British high society, according to a 1781 edition of the English Chronicle, Morris "conducted himself in this new exaltation with so much moderation, affability and friendship that the family soon forgot the degradation the Duchess had been guilty of by such a connexion [sic], and received her spouse into their perfect favour and esteem.

[19] After his father's death, Morris received half of his estate, which partially consisted of extensive landholdings in Westchester County, New York.

[20] When she died in 1789, the life interest passed to Morris, who eventually sold it to Gouverneur along with the New York landholdings he had received from his father.