Lord Wellesley now determined to crush Tipu Sultan, and finally annihilate the power which the French officers were building up in India by taking service with Nizam Ali Khan and other native princes.
Edmonstone was by his chief's side throughout this important year, and translated and published the documents found in Tippoo's palace, which formed the principal justification of the English attack upon him.
That the whole policy of Lord Wellesley in making the company the paramount power in India by means of his system of subsidiary treaties was largely due to Edmonstone there can be no doubt, though he modestly kept in the background.
On 1 January 1801 he was appointed secretary to the government of India in the secret, political, and foreign department, and he played as important a part in forming the plans which were to crush the Marathas as he had done in the war against Tippoo Sultan.
He was elected a Fellow of the Royal Society in 1826 as "an East India Director, and late Vice President of the Supreme Government of Bengal, (of 49 Portland Place) a Gentleman eminently versed in Oriental Literature and much attached to Science.