John Blackall (1771–1860) studied medicine at St Bartholomew’s Hospital and later practised in his native Exeter. In 1813 Blackall published his well known book, 'Observations on the Nature and Cure of Dropsies'. The work ran to four editions and gained a European reputation for its author. The cause of dropsy had not been previously understood and Blackall was the first to classify the disease by the amount of albumin in the urine. Blackall was said to have diagnostic powers of the highest order, and his practice in the west of England was extensive and lucrative. He did not retire from medicine until he was 80.

The portrait was produced by Ramsay Richard Reinagle, an English portrait, landscape and animal painter.