He seems to have entered the army in 1727 and served in Gibraltar and Flanders, subsequently taking part in the Battle of Culloden. In 1748, with the rank of major and the reputation of an experienced soldier, he went out to India to command the East India Company's troops. Dupleix's schemes for the French conquest of southern India were on the point of taking effect, and not long after his arrival at Fort St David, Lawrence was actively engaged. He successfully foiled an attempted surprise by French troops at Cuddalore, but was captured by a French cavalry patrol at "Ariancopang" (modern Ariankuppam) whilst leading forces to assist Admiral Edward Boscawen in enforcing the Siege of Pondicherry in 1748. He was kept prisoner by the French until the peace of Aix-la-Chapelle.