At the age of sixteen he won a silver palette in a competition run by the Society of Artists of Great Britain, and at eighteen was enrolled at the prestigious Royal Academy.

[1]: 80–82 In 1800, whilst still a probationary student in his first year, Westall was approached by Sir Joseph Banks to serve as landscape and figure painter to a voyage of exploration under Matthew Flinders, aboard HMS Investigator.

The position had first been offered to Julius Caesar Ibbetson, who declined; and then William Daniell, who accepted but subsequently pulled out.

[1]: 83–85  Elisabeth Findlay reconciles these claims by suggesting that Daniell "contrived" to have West put Westall's name forward.

[2] Westall's nomination was approved by Banks; thus Westall, at just 19 years of age, was appointed to what has come to be regarded as one of the notable scientific expeditions ever undertaken,[citation needed] as a member of a team of scientists that included botanist Robert Brown and botanical artist Ferdinand Bauer, both now revered as amongst the very best in their respective fields.

The following day Westall accompanied Bauer and Bell towards Cape Town, while Good and Brown climbed Table Mountain.

[8] As with Madeira, Westall was delighted with the landscapes on offer at the Cape, and worked conscientiously, making some highly detailed sketches.

Later that day he went with Flinders and others, firstly to examine Seal Island and search for a bottle and parchment that George Vancouver had left there ten years previously.

On 23 December Westall was one of a large party who set off on a grueling two-day overland expedition to Torbay Inlet and back.

During there ten-week hiatus there, he produced a great deal of work, including no fewer than thirteen detailed drawings of the Hawkesbury River, with which he was much taken.

Anchoring in Port Bowen on 21 August, the scientists went ashore to explore, and Flinders offered to name the highest mountain over whoever reached the peak first.

Within the island's rock shelters, they discovered an array of painted and stenciled patterns and Flinders enlisted Westall to record these images.

The third person of the band was twice the height of the others, and held in his hand something resembling the whaddie, or wooden sword of the natives of Port Jackson; and was probably intended to represent a chief.

Arriving back at Port Jackson in June 1803, Investigator was condemned, and Flinders decided to return to England to request a new ship.

As he was on the British government payroll at the time, he had no right to do so without permission, and must have known it, since, just before departing for India, he wrote a long letter to Banks justifying his travel plans.

In doing so he complained about the monotony of the Australian landscape, declared that he would not have agreed to the position if he had known that the voyage was confined to Australia alone, and hinted that he had the right to go to India as compensation for the failure of the Investigator to stop anywhere interesting.

When work on Flinders' A Voyage to Terra Australis got underway in 1811, it was Westall's oil paintings that became the basis of the engravings to be published therein.

In 1811 Westall published Foreign Scenery, a collection of landscapes depicting Madeira, the Cape of Good Hope, China and India.

He also worked for John Murray, such as several contributions to A Picturesque Tour of the River Thames (for which he shared authorship with Samuel Owen 1828).

[22] Supporting his family became the prime imperative of Westall's later life, and it is said that he often complained that he had sacrificed the chance of fame and success in order to earn a steady income in illustration.

He has also been criticised for his choice of subjects: his primary task was to record landscapes, but in the latter half of the voyage he mostly neglected them in favour of portraying people and events.

There was an expectation that Westall's pictures would serve as accurate objective records, and in many cases they are: his coastal profiles in particular have been praised for their accuracy.

Examples include his Entrance to Port Lincoln from behind Memory Cove, February 1802, which superimposes the foreground from one sketch of Port Lincoln upon the background of another; and his Part of King George Sound, on the South Coast of New Holland, which is based upon his drawing of King George's Sound, but has a completely revised foreground, including the insertion of a Eucalyptus that Westall sketched at Spencer Gulf, 1800 kilometres to the east.