After his return to Syria Barker undertook a journey to the scarcely known sources of the Orontes, no account of which, until the communication of his 'Notes' to the Geographical Society of London in 1836, had ever been published.
Barker was for 'many years resident at Tarsus in an official capacity'—in the list of members of the Syro-Egyptian Society of London for 1847–8 he is designated, probably by mistake, as 'H.B.M.
In the course of the Crimean War Barker placed his knowledge of the oriental languages and character at the disposal of the British government, in whose service he died on 28 January 1856, 'of cholera, at Sinope, on the Black Sea, aged 45', whilst employed as chief superintendent of the land transport depôt at that place.
He accumulated materials for his major work Lares and Penates (1853), which was edited by William Francis Ainsworth.
The Speech of His Royal Highness Prince Albert translated into the principal European and Oriental Languages,’ London, 1851.