An officer with the newly-founded Royal African Corps, Grant negotiated the purchase of St Mary's Island in the Gambia River from the King of Kombo in 1816, following the end of the Napoleonic Wars.
During his time as commandant, Grant founded the town of Bathurst on the island, which later became Banjul and the capital city of The Gambia as an independent country.
[2] Sir Charles MacCarthy, the Governor of Sierra Leone, dispatched Captain Alexander Grant, who at the time was an officer with the 2nd West India Regiment and was attached to the Royal African Corps.
Grant took with him a detachment of 75 soldiers of the Royal African Corps to establish whether it would be feasible to create a military stronghold on the Gambia River.
Lieutenant Colonel Thomas Brereton, the Governor of Senegal, approved the sandy pit at the extreme point of Banjulo, "probably more from a strategic view than a sanitary one"[2] as it was battered by the Atlantic waves, had a mangrove swamp behind it, but also commanded the mouth of the Gambia River.
This new capital on St Mary's Island was initially called Leopold, but the name was shortly afterwards changed to Bathurst by MacCarthy, under whom the town was designed.
[10] In 1823, Sierra Leone was chosen as the seat of government for the British West African Settlements, and annexed by Act of Parliament with a jurisdiction that included the Gambia.
[2] The soldiers on the island were ten to twelve days from headquarters and surrounded by warring tribes, who saw the British presence as "the first step towards their total dispossession.
It was a strip of territory one mile wide at the mouth of the Gambia River on the north bank, opposite Bathurst, and stretching from the ocean inland as far as the eastern boundary of the Kingdom of Barra.
Burungai Sonko, the King of Barra, agreed to the deal – which led to the British constructed Fort Bullen in the Ceded Mile over the next five years.
A short obituary in the London Courier and Gazette states that he "soon after fell a sacrifice to the effects of a climate that has been fatal to so many Europeans" and died on 29 September 1827.
The obituary went on to state that "for many years, when there was a post of difficulty or of danger, Colonel Grant was selected for it by the late Governor, Sir Charles McCarthy, whose confidence, esteem, and friendship, he possessed in the fullest measure.