Martin Cash, the son of Margaret and George Cash, was baptised on 10 October 1808 at Enniscorthy, County Wexford, Ireland. He worked there as a farm labourer until March 1827, when he was convicted of housebreaking. Sentenced to seven years' transportation, he served his time as a farm worker in the Hunter Valley of New South Wales, Australia, then in 1837 moved to Van Diemen's Land (Tasmania) with a neighbour's wife, Bessie Clifford. In 1840 he was sentenced to seven years' imprisonment for the theft of eggs valued at a shilling. In the next three years he escaped from gaol three times, on the last occasion from the Port Arthur gaol by swimming shark-infested seas with two comrades. The three outlaws survived by raiding homesteads and settlements to obtain food, money and ammunition.
Cash's good manners and penchant for robbing the rich earned him the sobriquet 'The Robin Hood of Van Diemen's Land'. He was recaptured, in mid 1843, after the news that his beloved Bessie had left him for another provoked him to look for her in Hobart. Sentenced to death for killing a constable while trying to evade arrest, Cash gained a last-minute reprieve and was sent to Norfolk Island for 10 years. Here he was a model prisoner. He was given some responsibility and was allowed to marry a fellow convict, Mary Bennett, on 14 May 1854. Later in 1854 he was granted a ticket of leave, returned to Van Diemen's Land, and became a constable at the Cascades penal settlement. He also worked as an overseer at the government gardens in Hobart, before being conditionally pardoned in 1856. Subsequently he moved to New Zealand, leaving his wife and an infant son in Tasmania.
In 1860 Cash came to public attention in Christchurch as a constable in the Canterbury Province Armed Police Force, which it appears he had joined the previous year. This gave him inside information useful in his main line of work, brothel-keeping. However, his colleagues had become suspicious of him, and united to convince officials that his identity and activities should be investigated. In March 1860 Cash was sacked and fined for keeping a brothel, amid fears that many others like him might have chosen to come to New Zealand after the decline of the Australian goldfields.
Details about Cash's activities after this date are scarce. He appears to have visited Tasmania at the end of 1860, but had returned to New Zealand by December 1862. According to one account he continued to operate several brothels in Christchurch's red light district, around Salisbury Street, including the notorious 'Red House', and regularly featured in the court news until unwelcome police attention encouraged him to try his luck on the Otago goldfields. There he is supposed to have been detected by the Otago police, and 'advised' to leave the province. According to this story he soon returned to Christchurch, withdrew his ill-gotten savings (allegedly about £2,000) from the bank, and returned to Tasmania. Here in May 1863 he bought a small farm at Glenorchy, a few miles from Hobart, where he lived with his wife and son. Towards the end of his life he narrated his autobiography to James Lester Burke, who edited and published it in 1870 under the title The adventures of Martin Cash. He died on 27 August 1877 from 'Fatty degeneration of Heart with Inflammation of Stomach and Intestines accelerated by Intemperance'.