Thomas was the son of John Sheppard Daniell, the lessee of the Swan Inn at Chertsey. In 1763 he was apprenticed to a coach-builder, a Mr Maxwell, where he learnt the elementary skills of painting.
After completing his apprenticeship in 1770, he worked for several years for Charles Catton, a coach-painter to George III. During this time he felt the urge to become a professional artist and entered the Royal Academy Schools. Between 1772 to 1784 he exhibited thirty pictures at the Royal Academy, from flower-pieces and portraits to literary subjects.
During the early 1780s there were few opportunities for landscape painters, as portrait painting dominated the English scene. Thomas was finding it difficult to establish himself whilst also gaining heavy family responsibilities. His brother who succeeded their father as landlord of the Swan, had died in 1779, leaving a widow to run the business and bring up her five children. To ease the situation, Thomas took over the care of his nephew William, who joined him in London to assist with his painting.
Encouraged by tales of fortunes being made by artists working in India, Thomas gained passage with the East India Company as an engraver with 15 year old William as his assistant. They departed from Gravesend in April 1785 bound for Canton. From China they gained the three-month passage to back to India, arriving in Calcutta early in 1786. They quickly made a name for themselves publishing their aquatints of the colonial city. From the proceeds of their sales, they journeyed to the north, south and west to discover and sketch the ‘real’ India with its temples, tombs and picturesque countryside.
Their route took them up the River Hooghly from Calcutta, then up the River Ganges to the foothills of the Himalayas. Then on to Madras and the south, before completing their journey to Bombay and the west.
William kept a diary for most of this time, recording their travels. He records his delight at discovering the footprint of a rhinoceros. In addition to the diary their movements can be traced from the dates and titles carefully inscribed on the backs of their pencil and watercolour drawings. They sketched many of the major sites along their route, including the Taj Mahal, pitching their tents directly opposite the monument itself. At Anupshaha they took part in a tiger hunt, for which William cleaned his gun and pistols in readiness, but unfortunately for William they did not see a single tiger and missed hitting a few hog deer.
They returned to England in 1794 and spent the following years producing six volumes of aquatints and exhibiting their oil paintings regularly at the Royal Academy. Their work was hugely popular and influenced a generation of china, wallpaper and building designers with their scenes of India. Their work embodied the taste of the time for the ‘picturesque, exotic and sublime’.