Ross was born in Ireland to Maj. David Ross, an officer in the Seven Years War and his mother was half-sister to the Earl of Charlesmont. He was educated at Trinity College, Dublin and joined the army as a ensign in 1789. He fought at the Battle of Krabbendam in the Netherlands, Alexandria, Egypt, the Battle of Maida, Scylla Castle, in the Peninsular War at Corunna and the Battle of Pamplona.

He had been promoted to Lieutenant-Colonel before Corunna. In 1810, Ross was made a colonel as well as aide-de-camp to the king. He fought in Spain under Wellington in 1812, at the battles of Vittoria, Roncesvalles, and the Sauroren.

After the conclusion of the war with Napolean, Ross sailed to North America as a Major-General to take charge of all British troops off the east coast of the United States. Ross personally led the British troops in the attack on the Americans at the Battle of Bladensburg on August 24, 1814, where the American army quickly collapsed. Moving on from Bladensburg, Ross captured Washington, D.C with little resistance. Ross insisted on only destroying public property when he ordered the burning of Washington, including the destruction of the Capitol and the White House.

Ross then organized an attack on Baltimore, Maryland. His troops landed at North Point, twelve miles from the city. During the march, the troops encountered American skirmishers and Ross rode forward to personally direct his troops. An American sniper shot him through the right arm into the chest. Two Americans, Dan Wells and Henry McComas are credited as the sniper team although both were killed in the engagement. Ross dies within minutes.