Jardine then persuaded the British Foreign Secretary Lord Palmerston to send warships to China to enforce a judgment for reparations and to preserve free trade. The hostilities that ensued became known as the First Opium War.
The Chinese lost and were forced to sign a treaty on August 29, 1842, which awarded the British $6 million in reparations, opened the ports of Canton, Amoy, Foochow, Ningpo, and Shanghai, and ceded the island of Hong Kong to Britain.
Jardine Matheson purchased the first plot of land to be sold in Hong Kong and promptly moved its offices there. The colony's first governor, Sir Henry Pottinger, endorsed the opium trade (in defiance of Queen Victoria) and later won the support of Parliament, which viewed the opium trade as a method to reduce the British trade deficit with China.
When the company's opium boats sailed into Hong Kong they were greeted by a cannon salute. Jardine Matheson profited greatly from its privileged position in Hong Kong, and through the strength of its opium trade, began to develop commercial interests throughout the region.
Jardine Matheson became known among the local Chinese as a hong (the word implies "big company" but has no relation to the name Hong Kong), and its chairman became known as a taipan, literally a "big boss."
During this period Thomas Keswick, also from Dumfriesshire, married Jardine's niece and was subsequently taken into the Jardine family business. Their son William Keswick established a Jardine Matheson office in Yokohama, Japan in 1859 and later became a leading figure in company management. The Keswick family grew in influence within the company, largely displacing the Matheson interests.