Mary Ann Robson was born on 31 October 1832 at Low Moorsley (now part of Hetton-le-Hole in the wider Houghton-le-Spring, part of the City of Sunderland), to Michael Robson, a colliery sinker, and Margaret, née Londsale, and baptised at St Mary's, West Rainton on 11 November. Her sister, Margaret, was born in 1834 but lived only a few months. Her brother, Robert, was born in 1835.
Soon after the move, Mary Ann's father fell 150 feet (46 m) to his death down a mine shaft at Murton colliery in February 1842. Her father's body was delivered to her mother in a sack bearing the stamp 'Property of the South Hetton Coal Company'. As the miner's cottage they inhabited was tied to Michael's job the widow and children would have been evicted. In 1843, her mother married George Stott (1816–1895), also a miner. At the age of 16, Mary Ann left home to become a nurse at the nearby village of South Hetton, in the home of Edward Potter, a manager at Murton colliery. After all of the children had been sent to boarding school in Darlington over the next three years, she returned to her step-father's home and trained as a dressmaker.
In 1852, at the age of 20, Mary Ann married colliery labourer william Mowbray at Newcastle Upon Tyne register office; they soon moved to South West England. At the time of her trial, there were reports of four or five of their children dying young while they were living away from County Durham. None of these deaths are registered, but this was not compulsory until 1874. The only birth recorded was that of their daughter, Margaret Jane, born at St Germans in 1856.
William and Mary Ann moved back to North East England, where william worked as a fireman aboard a steam vessel sailing out of Sunderland, then as a colliery foreman. Another daughter, Isabella, was born in 1858, and Margaret Jane died in 1860. Another daughter, also named Margaret Jane, was born in 1861 and finally a son, John Robert william, was born in 1863, but died a year later from gastric fever.
One of her patients at the infirmary was an Engineer, George Ward. They married at St Peter's Church, Monkwearmouth on 28 August 1865. Ward continued to suffer ill health and died on 20 October 1866 after a long illness characterised by paralysis and intestinal problems. The cause of death recorded on his death certificate is that of English cholera and typhoid. The attending Doctor later gave evidence that Ward had been very ill, yet he had been surprised that his death was so sudden. Once again, Mary Ann collected insurance money in respect of her husband's death.
James Robinson was a shipwright at Pallion in Sunderland, whose wife, Hannah, had recently died. He hired Mary Ann as a housekeeper in November 1866. A month later, when James' baby, John, died of gastric fever, he turned to his housekeeper for comfort and she became pregnant. Then Mary Ann's mother, living in Seaham Harbour, County Durham, became ill with hepatitis, so she immediately went to her. Although her mother began to recover, she also began to complain of stomach pains. She died at age 54 in the spring of 1867, nine days after Mary Ann's arrival. In 1867, Mary Ann's stepfather George Stott married his widowed neighbour, Hannah Paley.
Robinson married Mary Ann at St Michael's, Bishopwearmouth on 11 August 1867. Their first child, Margaret Isabella (Mary Isabella on her baptismal record), was born that November, but she became ill and died in February 1868. Their second child George was born on 18 June 1869.
Cotton and Mary Ann were bigamously married on 17 September 1870 at St Andrew's, Newcastle Upon Tyne and their son Robert was born early in 1871. Soon after, Mary Ann learnt that her former lover, Joseph Nattrass, was living 48 kilometres (30 mi) away in the County Durham village of West Auckland, and was no longer married. She rekindled the romance and persuaded her new family to move near him. Cotton died in December of that year, from "gastric fever." Insurance had been effected on his life and those of his sons.
Frederick Jr. died in March 1872 and the infant Robert soon after. Then Nattrass became ill with gastric fever and died just after revising his will in Mary Ann's favour.
Of Mary Ann's 13 children, only two survived her: Margaret Edith (1873–1954) and her son George from her marriage to James Robinson.
In 2015 ITV filmed a two-part television drama, Dark Angel, starring Joanne Froggatt as Cotton. The series also featured Alun Armstrong, Jonas Armstrong and Emma Fielding. The first part of the dramatisation was broadcast on 31 October 2016, the second on 7 November. The drama was inspired by the book Mary Ann Cotton: Britain's First Female Serial Killer by David Wilson, a criminologist.
The ITV two-part television drama, Dark Angel, was broadcast over two hours on PBS on 2018 March 25, in the United States.
Mary Ann’s first port of call after Charles' death was not the Doctor but the insurance office. There, she discovered that no money would be paid out until a death certificate was issued. An inquest was held and the jury returned a verdict of natural causes. Mary Ann claimed to have used arrowroot to relieve his illness and said Riley had made accusations against her because she had rejected his advances.