Captain James Colnett (c. 1753 – 1 September 1806) was a Royal Navy officer, explorer and a fur trader. He served under James Cook during Cook's second voyage of exploration. Later he led two private trading expeditions that involved collecting sea otter pelts in the Pacific Northwest of North America and selling them in Canton, China, where the East India Company maintained a trading post. Wintering in the recently discovered Hawaiian Islands was a key component of the new trade system.

Colnett is remembered largely for his involvement in the Nootka Crisis of 1789—initially a dispute between British traders and the Spanish Navy over the use of Nootka Sound on Vancouver Island that became an international crisis that led Britain and Spain to the brink of war before being peacefully resolved through diplomacy and the signing of the Nootka Conventions.

Due to Colnett's central role in the initial incident that sparked the international crisis, Colnett's account of his second fur trading voyage, including the events at Nootka Sound in 1789, was published in 1940, as part of the Champlain Society's General Series. His first trading voyage journal remained unpublished until 2005.

Colnett was born in Devon at Devonport in 1753, and was baptised on 18 October at Stoke Damerel parish church, Plymouth. His parents were James and Sarah (née Lang) Colnett. He had two older sisters and one younger brother. Very little is known about his life until he joined the Royal Navy as an able-bodied seaman in 1770.

Colnett joined the Royal Navy in June 1770, initially serving as an able seaman aboard HMS Hazard, and then aboard HMS Scorpion as a midshipman under Lieutenant James Cook from September until December 1771, when both Cook and Colnett moved to HMS Resolution. Colnett served as a midshipman during Cook's second voyage to the Pacific Ocean between 1772 and 1775. After returning to England in 1775, Colnett continued to serve in the Royal Navy during the American War of Independence, being appointed gunner aboard HMS Juno on 1 January 1776 and then as master of HMS Adventure. He rose in the ranks, passing his lieutenant's examination on 4 February 1779, and ten days later, on 14 February, he was appointed third lieutenant of HMS Bienfaisant. He was with Bienfaisant until 1783, when he joined HMS Pegase as her first lieutenant. On 17 August 1786 he went on half pay as work for naval officers fell following the end of hostilities.

Between 1786 and 1791 Colnett led two private fur-trading ventures. With the Royal Navy's approval and a leave of absence he was first given command of a two-vessel fur trading expedition to the Pacific Northwest coast, Hawaii, and China. The vessels included Prince of Wales and Princess Royal. Afterwards, a second expedition was organized with the Argonaut and the Princess Royal. The second expedition culminated in the Nootka Crisis. The first voyage was under the aegis of the London-based King George's Sound Company, first known as Richard Cadman Etches and Company, which owned the ships. The second was a joint venture of the King George's Sound Company and John Meares and his partners. Both companies were exploring the possibilities of collecting sea otter pelts along the Pacific Northwest coast, via trade with the indigenous peoples, and selling the goods in China. The idea had its origins in Cook's third voyage, during which sea otter pelts obtained along the northwest coast of America, from Nootka Sound northwards, were sold for high prices and great profit in Canton.

During the first fur-trading venture Colnett was in command of a two-vessel expedition. Colnett himself was captain of the 171-ton ship Prince of Wales. The second vessel was the 65-ton sloop Princess Royal, under Charles Duncan. The ships were owned by the King George's Sound Company, or Richard Cadman Etches and Company, and operated under licenses from the South Sea Company and the East India Company, which had a monopoly on British trade in the Pacific Ocean. The two ships left England on 23 September 1786, rounded Cape Horn, and reached the Pacific Northwest late in the summer of 1787. After trading for furs with the indigenous peoples in the vicinity of the Haida Gwaii archipelago, Aristazabal Island, and Banks Island, Colnett and Duncan sailed to the Hawaiian Islands where they spent the winter. While on the coast of present-day British Columbia they had a series of first contact encounters with some of the Kitkatla Tsimshian. In Hawaii they were involved in several violent conflicts with the islanders, including one at Waimea Bay, during which between five and fourteen Hawaiians were killed.

During his voyage, Colnett became the first European to see parts of southern Haida Gwaii. Juan Pérez had visited northern Haida Gwaii in 1774, but had not gone ashore. Colnett and his crew were among the first Europeans to set foot on the islands. They were also the first British explorers to contact the Tsimshian and southern Heiltsuk people.