[2] By 1807 Jackson's reputation as a portrait painter had become established, and he made the transition to oils steadily, if not easily, regularly forwarding paintings to Somerset House.

After a visit to the Netherlands and Flanders with Edmund Phipps in 1816, he accompanied Sir Francis Chantrey on a trip to Switzerland, Rome, Florence and Venice in 1819.

[2] Jackson was a prolific portraitist, strongly showing the influence of Sir Thomas Lawrence and Henry Raeburn in his work.

[3] His sitters included the Duke of Wellington, the explorer Sir John Franklin and some noted Wesleyan ministers.

John's first daughter, Maria Rosa Jackson married Marmaduke Brewer and she later ran a school in Monmouthshire.