After his death, his wife, Florence Maybrick, was convicted of his murder by poisoning in a sensational trial. The "Aigburth Poisoning" case was widely reported in the press on both sides of the Atlantic.
In 1880, Maybrick returned to the company's offices in England. Sailing from New York on 12 March 1880, he arrived in Liverpool six days later. During the journey he was introduced to Florence (Florie) Elizabeth Chandler, the daughter of a banker from Mobile, Alabama, and their relationship quickly blossomed. Despite the difference in their ages – he was 42 to her 18 – they began to plan their wedding immediately.
The wedding was delayed until 27 July 1881, when it took place at St James Church, Piccadilly, London. The couple returned to Liverpool to live at Maybrick's home, "Battlecrease House" in Aigburth, a suburb in the south of the city.
They had two children: a son, James Chandler ("Bobo"), born in 1882 and a daughter, Gladys Evelyn, born in 1886.
Maybrick continued to divide his time between the American and the English offices of his company and this may have caused difficulties within his marriage. He also resumed his relationships with his many mistresses, while his wife conducted an affair with an Alfred Brierley, a cotton broker. It is possible Florence embarked upon this on learning of her husband's infidelity.
In April 1889, Florence Maybrick bought flypaper containing arsenic fom a local chemist's shop and later soaked it in a bowl of water. At her trial, she claimed that this method allowed her to extract the arsenic for cosmetic use. James Maybrick was taken ill on 27 April 1889 after self-administering a double dose of strychnine. His doctors treated him for acute dyspepsia, but his condition deteriorated. On 8 May Florence Maybrick wrote a compromising letter to Brierley, which was intercepted by Alice Yapp, the nanny. Yapp passed it to James Maybrick's brother, Edwin, who was staying at Battlecrease. Edwin, himself by many accounts one of Florence's lovers, shared the contents of the letter with his brother Michael Maybrick, who was effectively the head of the family. By Michael's orders Florence was immediately deposed as mistress of her house and held under house arrest. On 9 May a nurse reported that Mrs Maybrick had surreptitiously tampered with a meat-juice bottle which was afterwards found to contain a half-grain of arsenic. Mrs Maybrick later testified that her husband had begged her to administer it as a pick-me-up. However, he never drank its contents.
Maybrick's health deteriorated suddenly on 27 April 1889, and he died fifteen days later. The circumstances of his death were deemed suspicious by his brothers and an inquest, held in a local hotel, came to the verdict that arsenical poisoning was the most likely cause, administered by persons unknown.
Suspicion immediately fell on Florence and she was arrested some days later. She stood trial at Liverpool Crown Court and, after a lengthy hearing, the fairness of which was the subject of some debate in later years, she was convicted of murder and sentenced to death. The way in which the judge conducted her trial was questioned and this was probably the reason her sentence was commuted to life imprisonment, some of which she served in a prison in Woking, Surrey, and then at the "House of Detention" at Aylesbury, Buckinghamshire.
A re-examination of her case resulted in her release in 1904. She supported herself through various occupations until her death on 23 October 1941. From her initial incarceration until her death, she never saw her children again.