Born in Enniscorthy, County Wexford, Ireland, Cash was brought up in a wealthy family and was literate. His memoirs describe that he shot at a man in a jealous rage for making advances on his sweetheart, but records list the original crime as house breaking. He was sentenced to seven years penal transportation and left Cook Harbour on the Marquis of Huntly, arriving in Sydney Town on 10 February 1828. Cash received his ticket of leave and worked as a stockman in New South Wales, settling with Bessie Clifford. However, he became suspected of cattle stealing and relocated to Tasmania.
Martin and Bessie found employment around Southern Tasmania until once again Cash was accused of stealing from an employer. This time he was sentenced to seven years in a Hobart prison. He briefly escaped and 18 months was added to his time. Again he escaped and almost made it across the Bass Strait with Bessie but was caught and faced 10 years at Port Arthur, the so called escape proof colony.
His first attempt at escape from Port Arthur failed, however, he managed to swim across the so called shark-infested Eaglehawk Neck, the first person to do so. This experience would later prove useful as it earned him much respect from other prisoners.
On Boxing Day 1842 Martin Cash, George Jones and Lawrence Kavenagh absconded from a work party. Hiding in dense scrub land and with little food they made their way 15km to the neck. Swimming with their clothes tied in bundles above their heads, they made the other side, all three of them having lost their bundles. Now naked the trio robbed a road gang's hut for clothing, and began a twenty month spree of bushranging, robbing mail coaches, homesteads and inns.
The three became known as Cash and Co and their reputation grew, however in August 1843 Cash discovered his partner Bessie was with another man in Hobart. Enraged, Cash swore to kill them both and he and Kavanagh made their way to Hobart. Although disguised as sailors, they were quickly spotted and a gunfight ensued. After a police constable was shot by Cash and killed, the two were overpowered and tried for murder.
Cash was found guilty and sentenced to death by hanging, and Kavanagh, guilty of robbing a mail coach, was also sentenced to death, however, a last minute reprieve saw the men sent to Norfolk Island.
There he eventually became a trustee, and later a constable. He married in 1854, and was granted his ticket of leave later that year. Subsequently he travelled to Christchurch, New Zealand in 1860 and became a free man in 1863.
Cash died in his own bed in Glenorchy, Tasmania in 1877. During the late 1860s, he had dictated his autobiography to an amensuensis, James Lester Burke. This account, although often embellished, provides a fascinating insight into convict life. Buck Thor and Joan Dehle Emberg later transcribed this account from the original manuscript and released it as The Uncensored Story of Martin Cash.