Cornwallis was born in London, England, in 1738. He was the son of Charles Cornwallis, 5th Baron Cornwallis, and Elizabeth Hamilton. He was educated at Eton College and Cambridge University.
Cornwallis joined the British Army in 1756. He served in the Seven Years' War (1756-1763), during which he was promoted to colonel. In 1761, he was appointed governor of Nova Scotia.
In 1775, Cornwallis was sent to America to help put down the American Revolution. He was initially successful, winning several battles against the Americans. However, in 1777, he was defeated by George Washington at the Battle of Saratoga. This defeat was a turning point in the war, as it convinced France to ally itself with the Americans.
Cornwallis was captured by the Americans at the Battle of Yorktown in 1781. This defeat effectively ended the war in America. Cornwallis was released from captivity in 1782 and returned to England.
After the war, Cornwallis served as governor-general of India from 1786 to 1793. During his time in India, he oversaw the expansion of British rule and introduced several reforms, including the Cornwallis Code, which established a new system of law and administration.
In 1793, Cornwallis returned to England. He was created Marquess Cornwallis in 1792 and served as Master-General of the Ordnance from 1793 to 1805. He died in India in 1805.
Cornwallis is considered one of the most important British generals of the 18th century. He was a highly skilled commander who won several major victories against the Americans. However, he is also criticized for his arrogance and for his failure to understand the American Revolution.