At the age of twelve he was set to work making outlines of the city of Edinburgh from the top of the Calton Hill Observatory, and a few years later made the drawings for the view of London from Albion Mills.
He continued to be his father's chief assistant in the panoramas till the latter's death in 1806, when, as executor, he took over the business, and carried on the exhibitions for 20 years with great success.
At Palermo, he called on Sir William Hamilton, the English ambassador to the court of Naples, who introduced him to Lord Nelson, who, he wrote, "took me by the hand and said he was indebted to me for keeping up the fame of his victory in the Battle of the Nile for a year longer than it would have lasted in the public estimation" (Barker's memoranda).
[1] In about 1802 he married the eldest of the six daughters of Rear Admiral William Bligh, who commanded the Bounty at the time of the celebrated mutiny.
[1][3] His brother, Thomas Edward Barker, although not an artist, was also involved in running the family business, but later set up a rival panorama exhibition with the painter Ramsay Richard Reinagle at 168/9 The Strand, London.