Jack Jones joined the army as a drummer boy in 1884; thereafter, he served in five military campaigns – the Gordon Relief Expedition to the Sudan (1884–1885), the Anglo-Egyptian Reconquest of the Sudan (1896–1899), the Boer War (1899–1901), where after that he was promoted to Lance Corporal, and the First World War (1914–1918) (declaring in "The Deadly Attachment" that, "I haven't had this much fun since I was in the trenches in 1916!").

While some characters, such as Major Regan, comment on Jones' medals as a way of critiquing his age and fitness for service in the Home Guard, others such as Captain Square (from the rival Eastgate platoon) are quite complimentary; at one point Square (himself a veteran campaigner) tells Jones that he has "an illuminated history of the British Empire" on his chest.

He was so keen to join the Local Defence Volunteers that, despite his age (70), Captain Mainwaring instantly appointed him as the platoon's lance corporal.

In many episodes, Jones fondly recalls his participation in the Battle of Omdurman in the Sudan, facing the "Fuzzy Wuzzies" under the command of General Kitchener.

As an aged veteran, he is extremely fond of bayonet warfare ("the cold steel"), and usually meets any queries about this with the assertion that "they don't like it up 'em!

It is also noted that Jones once kept wicket behind the great cricketer Ranjitsinhji, who was "an Indian gentleman and upstanding man" until he "whipped his bails off".

In the fifth episode of series one ("The Showing Up of Corporal Jones"), he tells Major Regan (who is inspecting the platoon) that he is sixty years old.

Jones contracted malaria during his military service in the Egypt and the Sudan in the Season 4 Episode 14 extended Christmas special "Battle of the Giants!"

Jones uses odd turns of phrase such as "It would be more tasty for us to tell him" (instead of "tasteful"), and "I would go through fire and brimstone and treacle for you, sir".

at the top of his voice (usually at some inappropriate moment, such as when holding an armed landmine or hand grenade) until someone manages to calm him down to a state in which he is useful.

In one episode, "The Two and a Half Feathers" Jones has to confront his past when a former comrade from the Sudan, Private Clarke, joins the Walmington-on-Sea platoon.

After his courage is doubted by the town and the platoon, Jones later vindicates himself with the true story of what happened (which he had nobly held back to spare a third party unnecessary pain or scandal).

Although Jones' over-keen and sometimes bungled efforts sometimes annoy Mainwaring, the captain is nonetheless admiring of his ever-enthusiastic approach, and considers him one of his best men, often discussing matters with him and Wilson before addressing the rest of the platoon.

His relationship with Mainwaring is also doubtlessly improved by Jones' tendency to flatter his superior officer and remains steadfastly loyal to him.

Notably in the episode "The King was in His Counting House", Jones disdains Mainwaring's claim that his father was a renowned tailor and member of "The Master Tailors' Guild", by revealing that Mainwaring's father merely owned a "poky little drapery shop up a side alley" and sold poor-quality workman's trousers.