Following his move to London in 1762 Barrett rapidly established himself as the leading landscape artist working in oil paint.
In 1764  he was exhibiting at both the Free Society of Artists and the Society of Artists of Great Britain.
Barret was awarded the premium prize of 50 guineas for the  Large Landscape with Figures which he exhibited at the Free Society exhibition in 1764,  and this was purchased a year later by the Marquess of Rockingham for £100 guineas.
At the  Society of Artists he displayed four paintings including views on the Dargle and Powerscourt Waterfall, paintings that he must have brought with him from Ireland.
In 1768 a rift developed in the Society of Artists of Great Britain.
A faction led by Sir William Chambers, at the suggestion of Barret, petitioned the King for the foundation of the Royal Academy.
Barret is mentioned as a nominated member in the foundation document.
Barret specialised particularly in wild and mountainous natural landscapes; of the 31 paintings he showed at the Royal Academy between  1769 and 1782, more than a third depicted such scenery.
He very occasionally undertook portraits, an example of which is the portrait of William Constable at Burton Constable Hall.
He also painted a number of pictures of animals such as the water spaniel belonging to Lord Edward Bentinck, that was exhibited at the Society of Artists of Great Britain in 1768.

On arriving in London Barret was able to build on the contacts that he had made in Ireland and particularly with the political faction that had grown up around Marquess of Rockingham known as the Rockinghamites or Rockingham Whigs.
 Rockingham was to become prime minister in 1765–1766 and again in 1782.
The connection was through Edmund Burke, Rockingham’s private secretary and prominent Rockinghamites who commissioned paintings from Barrett were the Duke of Portland, the Earl of Albemarle and Sir George Colebrook.
His patrons were mainly the rich landowner who wished to have their estates and parks recorded.
Barret soon found himself with numerous commissions and it was rumoured that he was earning up £2000 a year, a princeley sum for an artist at the time.
Contemporary accounts suggest that Barret was a highly sociable character and got on well with people and other artists.
Even though Richard Wilson made disparaging remarks about both Barret and Gainsborough at the same time, Bodkin maintains that Wilson and Barret were personal friends.
It is noticeable that many of the landowners who patronised Barret were in the process of building impressive new mansions which would require large oil paintings to decorate the reception rooms.
The Duke of Portland at Welbeck Abbey, Sir Peter Leicester at Tabley and the Marquess of Rockingham were all employing Carr of York as an architect and this may provide a link between his early commissions after Barret arrived from Ireland.

Barrett gained patronage from the following:
Following his move to London in 1762 Barrett rapidly established himself as the leading landscape artist working in oil paint. In 1764  he was exhibiting at both the Free Society of Artists and the Society of Artists of Great Britain. Barret was awarded the premium prize of 50 guineas for the  Large Landscape with Figures which he exhibited at the Free Society exhibition in 1764,  and this was purchased a year later by the Marquess of Rockingham for £100 guineas. At the  Society of Artists he displayed four paintings including views on the Dargle and Powerscourt Waterfall, paintings that he must have brought with him from Ireland. In 1768 a rift developed in the Society of Artists of Great Britain. A faction led by Sir William Chambers, at the suggestion of Barret, petitioned the King for the foundation of the Royal Academy. Barret is mentioned as a nominated member in the foundation document. Barret specialised particularly in wild and mountainous natural landscapes; of the 31 paintings he showed at the Royal Academy between  1769 and 1782, more than a third depicted such scenery. He very occasionally undertook portraits, an example of which is the portrait of William Constable at Burton Constable Hall. He also painted a number of pictures of animals such as the water spaniel belonging to Lord Edward Bentinck, that was exhibited at the Society of Artists of Great Britain in 1768.
On arriving in London Barret was able to build on the contacts that he had made in Ireland and particularly with the political faction that had grown up around Marquess of Rockingham known as the Rockinghamites or Rockingham Whigs.  Rockingham was to become prime minister in 1765–1766 and again in 1782. The connection was through Edmund Burke, Rockingham’s private secretary and prominent Rockinghamites who commissioned paintings from Barrett were the Duke of Portland, the Earl of Albemarle and Sir George Colebrook. His patrons were mainly the rich landowner who wished to have their estates and parks recorded. Barret soon found himself with numerous commissions and it was rumoured that he was earning up £2000 a year, a princeley sum for an artist at the time. Contemporary accounts suggest that Barret was a highly sociable character and got on well with people and other artists. Even though Richard Wilson made disparaging remarks about both Barret and Gainsborough at the same time, Bodkin maintains that Wilson and Barret were personal friends. It is noticeable that many of the landowners who patronised Barret were in the process of building impressive new mansions which would require large oil paintings to decorate the reception rooms. The Duke of Portland at Welbeck Abbey, Sir Peter Leicester at Tabley and the Marquess of Rockingham were all employing Carr of York as an architect and this may provide a link between his early commissions after Barret arrived from Ireland.
Barrett gained patronage from the following:
George Barret Sr.