Thomas Addison was born in April 1793, but his exact birthdate is not known. He was born in Longbenton, near Newcastle upon Tyne, the son of Sarah and Joseph Addison, a grocer and flour dealer in Long Benton. He attended the local Thomas rutter school and then went to the Royal Free Grammar School in Newcastle upon Tyne. He learned Latin so well that he made notes in Latin and spoke it fluently.  Addison’s father wanted him to become a lawyer, but he entered the University of Edinburgh in 1812 as a medical student. In 1815 he received the degree of Doctor of Medicine. His thesis was on Dissertatio medica inauguralis quaedam de syphilide et hydrargyro complectens (Concerning Syphilis and Mercury).

Addison moved from Edinburgh to London the same year and became a house surgeon (a surgical resident) at the Lock Hospital. Addison was also a pupil of Thomas Bateman at the public dispensary. He began a practice in medicine while he was physician at an open ward reception on Carey Street.Thanks to his teachers, Addison became fascinated by diseases of the skin (dermatology). This fascination, which lasted the rest of his life, led him to be the first to describe the changes in skin pigmentation typical of what is now called Addison’s disease.

Addison’s memorable career as a physician and scientist is usually dated to 1817 when he enrolled as a physician pupil at Guy’s Hospital. Guy’s Medical School recorded his entrance as follows: “Dec. 13, 1817, from Edinburgh, T. Addison, M.D., paid pounds 22-1s to be a perpetual Physician’s pupil.” Addison obtained his licentiateship in the Royal College of Physicians in 1819 and some years later was elected a fellow of the Royal College.

Addison was promoted to assistant physician on 14 January 1824 and in 1827 he was appointed lecturer of materia medica. In 1835 Addison was joint lecturer with Richard Bright on practical medicine, and in 1837 he became a full physician at Guy’s Hospital. When Bright retired from the lectureship in 1840 Addison became sole lecturer. He held this position until about 1854–55. At that time, when medical students paid fees for separate courses of lectures, they searched throughout the city for the most attractive teachers. Addison was a brilliant lecturer. He attracted a large number of medical students to his lectures.

Thomas Addison was a superb diagnostician but rather a shy and taciturn man and had a small practice, at a time when physicians of his position usually had large practices. He was one of the most respected physicians at the Guy’s Hospital, where he exerted a great deal of influence, devoting himself almost wholly to his students and patients. He was described as the type of doctor who is always trying to discover the change in a piece of machinery rather than one who, like his contemporary Benjamin Guy Babington, regarded his patients as suffering, sensitive human beings.

Thomas Addison suffered from many episodes of marked depression. It would seem certain that depression contributed to his retirement in 1860. He wrote then to his medical students as follows: “A considerable breakdown in my health has scared me from the anxieties, responsibilities and excitement of my profession; whether temporarily or permanently cannot yet be determined but, whatever may be the issue, be assured that nothing was better calculated to soothe me than the kind interest manifested by the pupils of Guy’s Hospital during the many trying years devoted to that institution.”

Three months later, on 29 June 1860, he committed suicide. The day after his death the Brighton Herald recorded that:

“ “Dr Addison, formerly a physician to Guy’s Hospital, committed suicide by jumping down the area (i.e. the space between the front of the house and the street) of 15 Wellington Villas, where he had for some time been residing, under the care of two attendants, having before attempted self-destruction. He was 72 years of age, and laboured under the form of insanity called melancholia, resulting from overwork of the brain. He was walking in the garden with his attendants, when he was summoned in to dinner. He made as if towards the front door, but suddenly threw himself over a dwarf-wall into the area – a distance of nine feet – and, falling on his head, the frontal bone was fractured, and death resulted at one o’clock yesterday morning” ”

He was buried in the churchyard of Lanercost Priory. The hospital had a bust made of him, named a hall of the new part of the hospital for him, and perpetuated his memory with a marble wall table in the chapel.