As lieutenant, he served with the Guides in Lord Cornwallis's campaigns against Tippu Sultan; and eight years after, as a field officer, was surveyor-general with the army under Lieutenant-general Harris, which captured Seringapatam in 1799.

The scanty population had been nearly swept off by a measles epidemic a short time previously, and, although recruited by emigrants from England and by Chinese coolies, was in a wretched state.

The acts of the home authorities in suppressing the spirit traffic and other matters gave rise to great discontent, resulting in a mutiny in 1811, which was put down by the firmness of Beatson, who also introduced a better system of cultivation and many other beneficial measures.

After his return to England, he devoted much attention to experiments in agriculture at Knole farm and Henley in Frant, Sussex, near Tunbridge Wells.

She returned to family members in Edinburgh after his death and is buried in the churchyard of St John's on Princes Street.