Turner was born in Maiden Lane, Covent Garden, London, England. His father, William Gay Turner (27 January 1738–7 August 1829), was a barber and wig maker.His mother, Mary Marshall, became increasingly mentally unstable, possibly due in part to the early death of Turner's younger sister, Helen Turner, in 1786. Mary Marshall died in 1804, after having been committed in 1799 to the Bethlem Royal Hospital, a mental asylum otherwise known as 'Bedlam'.

Possibly due to the load placed on the family by these problems, the young Turner was sent to stay with his maternal uncle in Brentford in 1785, which was then a small town west of London on the banks of the River Thames. It was here that he first expressed an interest in painting. A year later he attended a school in Margate on the north-east Kent coast. By this time he had created many drawings, which his father exhibited in his shop window.

He entered the Royal Academy of Art schools in 1789, when he was only 14 years old and was accepted into the academy a year later. Sir Joshua Reynolds, president of the Royal Academy, chaired the panel that admitted him. At first Turner showed a keen interest in architecture but was advised to continue painting by the architect Thomas Hardwick (junior). A watercolour by Turner was accepted for the Summer Exhibition of 1790 after only one year's study. He exhibited his first oil painting in 1796, Fishermen at Sea, and thereafter exhibited at the academy nearly every year for the rest of his life.

Turner travelled widely in Europe, starting with France and Switzerland in 1802 and studying in the Louvre in Paris in the same year. He also made many visits to Venice. On a visit to Lyme Regis, in Dorset, England, he painted a stormy scene (now in the Cincinnati Art Museum).

Important support for his work also came from Walter Ramsden Fawkes, of Farnley Hall, near Otley in Yorkshire, who became a close friend of the artist. Turner first visited Otley in 1797, aged 22, when commissioned to paint watercolours of the area. He was so attracted to Otley and the surrounding area that he returned to through his career. The stormy backdrop of Hannibal Crossing The Alps is reputed to have been inspired by a storm over Otley's Chevin while Turner was staying at Farnley Hall.

Turner was also a frequent guest of George O'Brien Wyndham, 3rd Earl of Egremont at Petworth House in West Sussex and painted scenes that Egremont funded taken from the grounds of the house and of the Sussex countryside, including a view of the Chichester Canal. Petworth House still displays a number of paintings.

As he grew older, Turner became more eccentric. He had few close friends except for his father, who lived with him for thirty years, eventually working as his studio assistant. His father's death in 1829 had a profound effect on him, and thereafter he was subject to bouts of depression. He never married, although his two daughters by Sarah Danby were born in 1801 and 1811.

He died in the house of his mistress Sophia Caroline Booth in Cheyne Walk, Chelsea on 19 December 1851. He is said to have uttered the last words "The sun is God" before expiring. At his request he was buried in St Paul's Cathedral, where he lies next to Sir Joshua Reynolds. His last exhibition at the Royal Academy was in 1850.

The architect Philip Hardwick (1792–1870) who was a friend of Turner's and also the son of the artist's tutor, Thomas Hardwick, was in charge of making his funeral arrangements and wrote to those who knew Turner to tell them at the time of his death that, "I must inform you, we have lost him."