He was commissioned in the King's forces in 1745 as a Captain and fought in the Jacobite rising against the Scots. He served with the 20th Regiment of Foot and the Marines. Later he is found in the West Indies as a Lieutenant-Colonel. He served until his appointment by Frederick Calvert, 6th Baron Baltimore as the proprietary Maryland colonial governor. (Following Samuel Ogle, who had died.) Horatio Sharpe was the brother of Lord Baltimore's guardian (William). He arrived in Maryland in August 1753.