In August 1779, at L’Orient, Stack embarked in the privateer Bonhomme Richard under Captain John Paul Jones, who appointed him 2nd Lieutenant, Continental Marines on 4 February 1779. On 23 September, Lt. Stack commanded Bonhomme Richard’s main top during her capture of HMS Serapis off Flamborough Head, Yorkshire. In his action report, Jones commended Stack for his bravery and crediting him with the victory.

Lt. Stack remained in Continental service until 1780. Later, he returned to France and was appointed to Dillon’s Regiment in the Irish Brigade, with which he accompanied the Marquis de Bouille’s expedition to the West Indies, where he participated in the reduction of Tobago, St. Kitts, Nevis and Monserrat.

Stack was promoted captain in 1789 and appointed Chevalier de St. Louis and Chevalier de Cincinnatus d’Amerique by Louis XVI. He was promoted major in 1791 and lieutenant colonel in 1793.

The Irish Brigade, then serving in the West Indies, refused to serve under the Committee of Public Safety and transferred to the British Service 1794. At their final reduction in 1798, LCol. Stack was placed on half pay. In 1801, he was promoted to colonel in command of the North Lowland Fencible Brigade which was broken up at the Peace of Amiens.

He traveled on leave a of absence to France, where he was arrested at the declaration of war and confined to the fortress at Biche. In 1803, while in captivity, he was promoted to brigadier general. In 1804, he was detected executing secret service work for the British government and sentenced to be shot together with Duc d’Enghien, but was reprieved at the last moment by the Emperor Napoleon.

In 1806, he was transferred to Verdun. Promoted major general in 1808 and lieutenant general in 1813, he was released by Louis XVIII in 1814 and returned to England.

Promoted to general in 1830, died at Calais, France, in December 1833.