Serving in the West India Regiments, Horton was posted to various locations within the British Empire, including Lagos, the Gambia, Sierra Leone and the Gold Coast and participated in the Anglo-Ashanti wars.

Horton wrote extensively on the medicine and botany of West Africa, and espoused African nationalism and pan-Africanism in opposition to racism by European writers.

[1] His father was James Horton Sr., an Igbo man who had been sold into slavery as part of the Atlantic slave trade before being liberated by the Royal Navy's West Africa Squadron and landed ashore at Freetown.

In 1855, alongside fellow Creoles William Davies and Samuel Campbell, he received a War Office scholarship to study medicine in Britain to prepare Horton for a career in the British Armed Forces, which at the time was looking for Black military personnel more acclimated to African environments to serve in Africa.

Horton studied at King's College London, and in 1858 published his dissertation, which was titled "On the medical topography of the west coast of Africa including sketches of its botany".

When he returned to Sierra Leone, Horton was posted to the neighbouring British colony of the Gold Coast, serving in the West India Regiments.

As part of his military career, he was posted to various locations within the British Empire, including Lagos, the Gambia, Sierra Leone and the Gold Coast.

[14] At the same time, Horton conducted his own medical science experiments in Africa, including an attempt to prove the presence of malaria in the miasmatic gasses of the Keta Lagoon.