John Thirtle (also written as Thurtle or Thurtell) (June 1777–30 September 1839) was an English artist, known for his work in miniaturism and watercolours. He was a leading member of the Norwich School of painters and the most talented of all the pupils of John Sell Cotman. A contemporary thought that his talents as a watercolourist surpassed those of both Cotman and John Crome. Thirtle's paintings of Norwich are considered to be outstanding in the history of watercolour painting.
The majority of Thirtle's watercolours are of his home city and the surrounding Norfolk countryside, many being riverside scenes. He exhibited only ninety-seven works, mainly in Norwich. His style, which was influenced by Thomas Girtin, John Crome and to a lesser extent by John Sell Cotman, was both technically accomplished and individual. His earlier landscapes were painted with a restricted range of buffs, blues and grey-browns, but he later developed a brilliancy of colour, producing works that included angular block forms. He published his Manuscript Treatise on Watercolour, mainly a reference manual for his own use. Unhappily, several of his watercolours have deteriorated over the years, because the indigo pigment that he used has since faded and reddened.
He was born in Norwich, where he lived for nearly all his life, and learnt the trade of a frame maker in London before returning home to Norwich, where he set up a frame-making business and continued to produce watercolours. He worked as a wood carver, a gilder and a drawing-master, and became a successful local businessman. In 1812 he married Elizabeth Miles, the sister-in-law of John Sell Cotman, but there were no children. He belonged to the Norwich Society of Artists from its inception in 1803 until its dissolution in 1833, and exhibited works there from 1806 to 1817, in time becoming its Vice-President. In 1816 he was one of a group of Norwich artists to secede from the Society. Because of his increasing ill health, his artistic output gradually declined. He died of consumption in 1839 and was buried in Norwich. His widow Elizabeth died aged 95, having outlived him for over forty years.