He was born at Sudbury, Soffolk, and went to London in about 1740, probably studying with the French engraver Gravelot. He returned to Sudbury in 1748 and in 1752 he set up as a portrait painter at Ipswitch. His work at this time consisted mainly of heads and half-length, but he also painted some small portrait groups in landscape settings which are the most lyrical of all English conversation pieces. His patrons were the merchants of the town and the neighboring squires, but when in 1759 he moved to Bath, his new sitters were members of Society, and he developed a free and elegant mode of painting seen at its most characteristic in full-length portraits.
In 1768 he was elected a foundation member of the Royal Academy, and in 1774 he moved permanently to London. Here, he further developed the personal style he had evolved at Bath, working with light and rapid brush-strokes and delicate and evanescent colors. He became a favorite painter of the Royal Family, even though his rival Reynolds was appointed King's Principal Painter.
Gainsborough sometimes said that while portraiture was his profession landscape painting was his pleasure, and he continued to paint landscapes long after he had left a country neighborhood. He produced many landscape drawings, some in pencil, some in charcoal and chalk, and he occasionally made drawings which he varnished. He also, in later years, painted fancy pictures of pastoral subjects.
Gainsborough's style had diverse sources. His early works show the influence of French engraving and of Dutch landscape painting; at Bath his change of portrait style owed much to a close study of van Dyck; and in his later landscapes, he is sometimes influenced by Rubens. But he was an independent and original genius, able to assimilate to his own ends what he learnt from others, and he relied always mainly on his own resources. With the exception of his nephew Gainsborough Dupont, he had no assistants and unlike most of his contemporaries he never employed a drapery painter.
He was in many ways the antithesis of Reynolds. Whereas Reynolds was sober-minded and the complete professional, Gainsborough (even though his output was prodigious) was much more easy-going and often overdue with his commissions, writing that 'painting and punctuality mix like oil and vinegar'. Although he was an entertaining letter-writer, Gainsborough, unlike Reynolds, had no interest in literary or historical themes, his great passion outside painting being music (his friend William Jackson the composer wrote that he 'avoided the company of literary men, who were his aversion... he detested reading'). Gainsborough and Reynolds had great mutual respect, however; Gainsborough asked for Reynolds to visit him on his deathbed, and Reynolds paid posthumous tribute to his rival in his Fourteenth Discourse. Recognizing the fluid brilliance of his brushwork, Reynolds praised 'his manner of forming all the parts of a picture together', and wrote of 'all those odd scratches and marks' that 'by a kind of magic, at a certain distance... seem to drop into their proper places'.