Blacker was born in Armagh, Northern Ireland where his family has an ancestral home in the barony of Oneilland East.

He obtained a commission in the Madras Cavalry in 1798, was made a cornet in 1799, and aide-de-camp to a Colonel Stevenson in the Wayanad district in 1800, and quartermaster-general in 1810.

[7] Andrew Waugh said that "Blacker, with the exception of Colonel George Everest, was the ablest and most scientific man that ever presided over this expensive department".

His correspondence with his father concerning military and political news, as well as his observations about Indian life and culture, was published in 1798.

[9] Blacker published a history of the Third Anglo-Maratha War, including discussion of the Battle of Khadki, in 1821.