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. He served in Deccan, 1817, and was promoted to lieutenant-colonel. Blacker took over from John Hodgson as Surveyor General of India in 1823.
In this capacity he made substantial contributions to the on-going Trigonometrical Survey of India.
He was stationed in Calcutta from 1823 until his death there from a fever in 1826. He was buried in South Park Street Cemetery in Calcutta.
Andrew Waugh said of him that "Blacker, with the exception of Colonel Everest, was the ablest and most scientific man that ever presided over this expensive department".