In 1797, he went to Constantinople where he became private secretary to Sir John Spencer Smith, the British ambassador to the Ottoman Empire.

[1] Upon his departure, the Aleppo consulship remained vacant for nearly a decade, until Nathaniel William Werry was appointed to the post in 1835.

[8] Barker proved himself unreliable during the first stages of the crisis between Western powers and Muhammad Ali Pasha, the viceroy of Egypt who was pursuing an expansionist policy at that time.

As a result, British Foreign Secretary Lord Palmerston replaced him as consul with a commissioned officer, Colonel Patrick Campbell.

[7] Barker spent his retirement years in Suedia (ancient Seleucia Pieria), on the banks of the Orontes River, near the city of Antioch.

[12] When an outbreak of cholera occurred in the north of Syria in 1848, a remedy was discovered by which many persons were cured even in the advanced stages of the disease.

Barker verified the efficiency of the remedy by personal observation, and once he was satisfied with the result, he went to great lengths to spread the knowledge of what he deemed an important discovery to the whole world.

[14] Barker and his wife Marianne had three sons and two daughters, all of whom possessed a great facility for acquiring languages, and became proficient Orientalists.