Thomas Girtin was born on February 18, 1775 in London, as the son of a wealthy brushmaker. His father died while Thomas was a child, and his mother remarried a Mr.Vaughan, a pattern-draughtsman. Girtin was apprenticed to Edward Dayes, a topographical watercolourist.
When he was still young Girtin became friends with J. M. W. Turner and the two teenagers were employed to colour prints with watercolour, which was the main use of the medium at that time. Girtin exhibited at the Royal Academy from 1794. His architectural and topographical sketches and drawings soon established his reputation. He went on sketching tours, visiting the north of England, North Wales and the West Country. By 1799 he had acquired influential patrons such as Lady Sutherland, and the art collector Sir George Beaumont.
In 1800 Girtin married Mary Ann Borrett, the sixteen year old daughter of a goldsmith, and set up home in St George's Row, Hyde Park. By 1801 he was a welcome houseguest at his patrons' country houses such as Harewood House and Mulgrave Castle, and was able to charge more for a painting. But his health was deteriorating.
In late 1801 to early 1802 he spent five and a half months in Paris, where he painted watercolours and made a series of pencil sketches which he engraved on his return to London. In the spring and summer of 1802, Girtin produced a panorama of London. It was notable for its naturalistic treatment of urban light and atmosphere.
Thomas Girtin died on November 9, 1802 in his painting room. The cause was variously reported as asthma.