The Cyprus mutiny took place on 14 August 1829 in Recherche Bay off the British penal settlement of Van Diemen's Land (now Tasmania, Australia). Convicts seized the brig Cyprus and sailed her to Canton, China, where they scuttled her and claimed to be castaways from another vessel. On the way, Cyprus visited Japan during the height of the period of severe Japanese restrictions on the entry of foreigners, the first ship from Australia to do so.

Several of the mutineers were eventually captured. Two of them, George James Davis and William Watts, were hanged at Execution Dock, London on 16 December 1830, the last men hanged for piracy in Britain. Their leader, William Swallow, was never convicted of piracy because he convinced the British authorities that, as the only experienced sailor, he had been forced to remain onboard and coerced to navigate the ship. Swallow was instead sentenced to life on Van Diemen's Land for escaping, where he died four years later.

Swallow wrote an account of the voyage including the visit to Japan, but this part of the journey was generally dismissed as fantasy until 2017, when he was vindicated by an amateur historian's discovery that the account matched Japanese records of a "barbarian" ship flying a British flag whose origins had remained a mystery for 187 years.

On 6 August 1829, the brig Cyprus, a government-owned vessel used to transport goods, people, and convicts, set sail from Hobart Town for Macquarie Harbour Penal Station on a routine voyage carrying supplies and convicts under a guard commanded by Lieutenant Carew, a British Army officer. There were 62 people on board, including wives and children of some personnel, and 31 convicts.

On reaching Recherche Bay, isolated from the main settlement, the vessel was becalmed. Convicts allowed on deck attacked their guards and took control of the brig. The convicts marooned officers, soldiers, and convicts who did not join the mutiny in Recherche Bay, without supplies. They were saved by a convict called Popjoy who constructed a makeshift boat or coracle using only the three pocket-knives they had, and sailed to Partridge Island with Morgan, a free man, where they got help.

Nineteen convicts sailed away in Cyprus, having appointed one of their number, William Swallow, the only one with sailing experience, as sailing master. The mutineers first sailed to New Zealand, and then on to the Chatham Islands. There they plundered the schooner Samuel of the seal skins her crew had gathered. From the Islands, Cyprus sailed for Tahiti, but then changed destination to Tonga. The mutineers landed at Keppel's Island, where Ferguson, the leader, and six others decided to remain. Swallow then sailed to Japan.

Swallow wrote an account of the voyage which included a visit to Japan before reaching Canton; this was generally dismissed as fantasy. However, in 2017 this account was compared with Japanese records of a visit by a British vessel off the town of Mugi, Tokushima on Shikoku in 1830, and matched in many points.

Makita Hamaguchi, a local samurai went disguised as a fisherman to check the ship for weapons, wrote an account of the episode which included watercolour sketches of the ship and its crew. Another samurai chronicler called Hirota noted the crew offered gifts, including an object he later drew which has since been identified as a boomerang. The mutineers were desperately low on water, firewood, and supplies, but were attacked and sent away by the Japanese, in line with the isolationist policy of the time.