Darwin was born at Elston. He studied medicine at the universities of Cambridge and Edinburgh, obtaining his MB from Cambridge in 1755. Darwin set up practice in Lichfield, where he soon established a reputation such that George III asked him to move to London to become his personal physician – an offer Darwin declined. He remained in Lichfield and founded, with friends, the Lunar Society of Birmingham – so called because of the monthly meetings held at members' houses. It included such eminent men as Joseph Priestley, Josiah Wedgwood, James Watt, and Matthew Boulton.

Darwin was something of an inventor, but is best remembered for his scientific writings, which often appeared in verse form. These were generally well received until the politician George Canning produced a very damaging parody of his work. This was part of a general campaign by the government against the Lunar Society for its support of the French and American revolutions, as well as its denouncement of slavery.

In his work Zoonomia (1794–96), Darwin advanced an evolutionary theory stating that changes in an organism are caused by the direct influence of the environment, a proposal similar to that put forward by Jean Baptiste Lamarck some 15 years later.

Darwin was the grandfather, by his first wife, of Charles Robert Darwin and, by his second wife, of Francis Galton.