In 1898 J. T. Maguire and his four sons – Alexander, David, Richard and Robert - left the Diamond Match Company of America to form Maguire, Miller & Co. In the 1900s Maguire worked on the White Phosphorus Prohibition Act of 1908, for which he was knighted in 1918. In 1919, with the death of two of his brothers and the retirement of another, he took over the directorship of the company and formed Maguire, Paterson and Palmer. His niece Isobel Maguire married Brigadier George Taylor (soldier) CBE, Distinguished Service Order & Bar.
In 1945 Maguire stayed in Upper Carlisle Road, Eastbourne. There he was treated by society doctor John Bodkin Adams, the suspected serial killer. According to Olwen Williams, Maguire's nurse, Adams plied the patient with whisky despite him being "an inebriate". Maguire soon moved back to London where he died 18 months later from "chronic alcoholism".