He efficiently served British political interests in the name of commercial enterprise, keeping a vigilant watch over the Sikhs with a view to checking them from extending their influence towards Shikarpur and Sindh. He also played an important role in the negotiations between Sir William Macnaghten and Maharaja Ranjit Singh which resulted in the Tripartite treaty. In 1838, he proceeded to Peshawar with the concurrence of the Lahore Darbar to win over the people of the Khaibar region, to the side of Shah Shuja'. He hobnobbed both with the Sikhs and the Afghans soliciting help for the Khaibar operations.
He remained at Peshawar till 1842. During the first Anglo-Sikh war Mackeson was with Sir Harry Smith's division in the field and was present at "Alival. In March 1846, he was appointed superintendent of the cis-Sutlej territory. In the second Anglo-Sikh war he was with Hugh Gough as Governor-General's agent. From 1851 to 1853, he served as commissioner at Peshawar, where he was assassinated by a local guardsman on 10 September 1853.
1. Fauja Singh, Military System of the Sikhs (1799-1849). Delhi, 186-1
2. Hasrat, B.J., Anglo-Sikh Relations (1799-1849). Ho.shiaipur, 1968
3. Buckland, O.K., Dictionary of Indian Biography. London, 1906