It was intended that he followed his father into the family business but, intent on a career in art, he moved to London in 1798, where he met artists such as J. M. W. Turner, Peter de Wint and Thomas Girtin, whose sketching club he joined, and whom he travelled with to Wales and Surrey.

[citation needed] The young Cotman was educated at Norwich Grammar School, and is recorded as starting there as a non-paying pupil on 3 August 1793.

"[5] A drawing from this period, House at St Stephen's Road, Norwich (1794), is considered to be the earliest surviving work by Cotman, sketched when he was 12.

His sketches at Rudulph Ackerman's print shop at 96 The Strand were studied by the Norwich artist John Thirtle when a young man.

[15] Their daughter Ann was born in July 1812 after the family moved to Great Yarmouth in April 1812, followed by three more sons, John Joseph Cotman, (Francis) Walter, and Alfred Henry.

[17] As part of his teaching, Cotman operated his own version of a watercolour subscription library, so that his pupils could take home his drawings to copy.

[13] From 1812 to 1823, Cotman lived on the Norfolk coast at Great Yarmouth, where he studied the shipping, and mastered depicting the form of sea waves.

[19] In 1817, 1818, and 1820, whilst Cotman was living in Great Yarmouth, he visited Normandy to make drawings of the landscape and buildings of the region.

The idea for Cotman to tour Normandy came from his friend Dawson Turner, who had visited the region in September 1815 with the British artist Thomas Phillips to view the works of art taken to Paris by Napoleon.

[21] Cotman went first to London, where he purchased a camera lucida from Sir Henry Englefield, and viewed the newly-installed Elgin Marbles at the British Museum.

The camera lucida was used for all three of Cotman's tours, but he seems to have struggled to use it to depict buildings accurately:[21] I was a week drawing the front [of Rouen Cathedral] with a camera lucida,... but not knowing how to use it, I so misused it that I am afraid my labour is entirely lost, from getting different focuses.Cotman sailed from Brighton to Dieppe on 18 July, and began exploring the area around Dieppe the following day.

[26] Upon returning home to Great Yarmouth, Cotman worked tirelessly to produce the etchings needed for Dawson Turner's Architectural Antiquities of Normandy, which was published in 1822.

[20] Cotman returned to Norwich in 1824, hoping to improve his financial position, and moved into a large house in St Martin's Plain, opposite the Bishop's Palace, where he built up a collection of prints, books, armour, and models of ships, to aid his compositions.

In January 1834, Cotman was appointed Master of landscape drawing at King's College School in London, partly on the recommendation of J.M.W. Turner.

In London, Cotman developed friendships with the artists James Stark, George Cattermole, Samuel Prout, and Cornelius Varley.

[31] Granted a fortnight's leave from King's College, he journeyed from London to Great Yarmouth by ship and then on to Norwich, ultimately staying in Norfolk for two months before returning to the capital.

[32] He produced some chalk drawings of church interiors,[33] and of the Norfolk countryside, the dates of which allow his journey around the county to be traced:[34] his sketches included Itteringham, 12 November and Storm off Cromer.

[41] Over 600 of Cotman's watercolours and drawings were bought by the Norwich curator James Reeve, who sold more than half of them to the British Museum in 1902.

[47] The architect Augustus Pugin, in his Specimens of Gothic Architecture (1823), mixed praise and criticism [the plates] are drawn and etched in a masterly style, but with a good deal of management, by which the subjects appear, in several instances, of grander character than really belongs to them...In some Plates also, the human figures are evidently below the size of life, and so exaggerate the size of the buildings they are placed against.

[47] The 1887 edition of the Dictionary of National Biography noted that Cotman's reputation had improved over time, and described him as "one of the most original and versatile of English artists of the first half of this century, a draughtsman and colourist of exceptional gifts, a water-colourist worthy to be ranked among the greater men, and excellent whether as a painter of land or sea".

[49][50] The art historians Lawrence Binyon and William Dickes both wrote extensively about Cotman's oil paintings and watercolours.