Elliot was assistant successively to the collector of Bareilly, the political agent at Delhi, and the collector of the southern division of Muradabad; secretary to the Sudder board of Revenue for the North-Western Provinces; and (1847) secretary to the governor-general in council for the foreign department. In this capacity he accompanied Lord Hardinge to the Panjab and drew up an admirable memoir on its resources. As foreign secretary he also visited the western frontier with Lord Dalhousie, on the occasion of the Sikh War, and negotiated the treaty with the Sikh chiefs relative to the settlement of the Panjab and Gujarat, and received the KCB for his services (1849). Throughout his official career he had devoted his leisure to study.