Thomas Plunket was born in 1785 in Newtown, Wexford, Ireland. He joined the 95th Rifles in May 1805. In 1807, he took part in the British invasions of the River Plate (1806–1807). During the 2nd Battle of Buenos Aires, the 95th Rifles were heavily engaged in street-fighting, during which Plunket killed around 20 Spanish troops while sniping from a rooftop with others from his unit. They retreated when Spanish artillery bombarded their position with grapeshot. Plunket also shot a Spanish officer waving a white handkerchief with the possible intention of inviting a truce. This resulted in further Spanish artillery bombardment, which brought about the British surrender.^[1]

Plunket is mainly remembered for a feat at the Battle of Cacabelos during Moore's retreat to Corunna in 1809. Plunket ran forward about 90 metres (100 yd), lay down in a supine position in the snow, and shot the French Général de Brigade Auguste-Marie-François Colbert with his Baker rifle.^[2][3] Before returning to his lines he reloaded and shot down Colbert's aide-de-camp, Latour-Maubourg, who had rushed to the aid of the fallen general, which showed that the first shot had not been a fluke. Plunket only just made it back to his lines before being charged down by a dozen cavalry troopers, but the deaths of the two officers were sufficient to throw the pending French attack into disarray.^[3][2][4] The shots were "from a range that seemed extraordinary to the" men of the 95th Rifles,^[5] who were trained to shoot targets with a Baker Rifle at 180 metres (200 yd) and whose marksmanship was far better than the ordinary British soldiers who were armed with a Brown Bess musket and only trained to shoot into a body of men at 50 metres (55 yd) with volley fire.^[2][3][6]

In 1817, Plunket was discharged from the 95th after recovering from a head wound at the Battle of Waterloo. Awarded a pension of 6d a day, he soon enlisted back into the army in a line regiment, 41st Foot.^[1] The regiment was being inspected by his former commanding officer, General Sir Thomas Sydney Beckwith when the general recognised Plunket and inquired into what had happened to him. He was invited to the officers' mess that night and the next day was promoted to corporal, and soon also had his pension raised to one shilling a day with Beckwith's influence.^[7] He later renounced his pension in exchange for four years' pay and land in Canada, but he returned to England after a year, considering the land unsuitable.

Plunket and his wife returned to the United Kingdom and, nearly destitute, made a small living as itinerant traders. Plunket died suddenly at Colchester in 1839. Several retired officers in the town heard about the death and recognized his name; as a result, they took up a collection for his widow and paid for his funeral and gravestone.^[2][1]

• Costello, Edward (1852). The adventures of a soldier; or, Memoirs of Edward Costello, narratives of ... p. 9. —"Colonel Beckwith [,the 95th CO,] broke the silence, by calling out, 'Private Thomas Plunket, step into the square!' All eyes, it is needless to say, were eagerly fixed upon Plunket, as he halted, with his rifle shouldered, in the finest position of military attention, within a few paces of his Colonel. 'Here, men,' exclaimed the commanding officer, pointing to Plunket, 'here stands a pattern for the battalion!'"
• Rutherford-Moore, Richard. "Plunket's Shot". Archived from the original on 11 October 2012.