He became a regimental commander in 1761, serving with distinction at the battle of Vellinghausen in northern Germany during the Seven Years War, and again the following year in two more major engagements. .
In 1775, Cornwallis volunteered for service in America, even though he objected to British policies in the colonies. He voted against the Stamp Act in 1765, one of only six members of the House of Lords to do so. He voted in opposition to the Declaratory Act, which affirmed as absolute Parliament's authority over the colonies. Cornwallis demonstrated a history of opposition to the policies that initiated the Revolutionary War, believing that England did not have the right to tax the colonies. It was his sense of duty, and the prospect of serving with one his fellow officers in the Grenadier Guards, Henry Clinton, that aided as motivation for him to go to America. Once in America he was less sympathetic, and came to the mind that the war was one of opinion and inducement. In a letter to Vice Admiral Arbuthnot, commander of the Royal Navy's North American station, Cornwallis wrote that there " is but one way of inducing the violent rebels to become our friends, and that is by convincing them it is in their interest to be so. " .
The reputation of Cornwallis as a military leader was much like that of George Washington. He was completely committed to being a soldier. The military was his life, not just a profession. He did not believe in conceit, or a title, accepting as true that reputation was of the utmost importance. Like Washington, he led assaults at the front of his army, having horses shot from underneath him during battle. Cornwallis demonstrated genuine concern for the welfare of his men, eating the same food, sleeping in the same conditions, and suffering the same deprivations during a march. To Cornwallis, his family was his regiment, and his army.
Sir Henry Clinton personally welcomed Cornwallis upon his arrival in America.
