He served as Captain of the Foretop, a Petty Officer rank, on HMS Terror during the 1845 Franklin Expedition, which sought to chart the Canadian Arctic, find the Northwest Passage, and make scientific observations.

While Peglar's remains have not been identified, several of his personal effects were found with a skeleton by Francis Leopold McClintock, which constitute among the only written materials known to belong to members of the expedition.

[2] In September 1825, one month after his admittance into the Marine Society, Peglar was sent to HMS Solebay, a shoreside training station where he was initiated into the navy, being trained in rowing, going aloft, managing sails, making knots and splices, using equipment such as the compass, and working guns and other arms, as well as in reading, writing, habituation to subordination and naval discipline, and religious instruction, going to Deptford Church on Sundays.

[2] Peglar was discharged "with a good character" from Solebay on 14 December 1825, and sent aboard the tender Star to join HMS Clio, stationed in the Chatham Dockyard.

[2] While aboard Rattlesnake, commanded by Captain John Leith, Peglar called upon most ports in the West Indies, including Inagua, Port-au-Prince, Havana, Montego, Santiago de Cuba, Chagres, as well as Bermuda and Halifax, before returning to England and paying off in September 1827 at the Woolwich Dockyard.

[2] On 3 September 1827, only days after returning to England, Peglar joined the ship HMS Perseus, stationed at the Tower of London and commanded by Captain James Crouch.

[2] After being discharged, Peglar entered the service the East India Company, and sailed under Thomas Larkins aboard the Marquis Camden, bound for St. Helena, as it was bringing Brigadier General Charles Dallas, who was appointed governor.

Successfully out of the Royal Navy again, he rejoined Thomas Larkins aboard Marquis Camden which sailed for St Helena, Bombay, Penang, Singapore, and Macau.

He did not mention this service in his report due to it being unsatisfactory: he was disrated to ordinary seaman in January 1833, confined in irons, and punished with two dozen lashes for drunkenness and mutinous conduct.

[2] In his account he noted only one event, when the schooner Royal Tiger fired upon the poop deck of Marquis Camden, killing the Chief Mate John Fenn, who was buried the next day on shore.

[2] Peglar joined, on 4 April 1834, the 18-gun brig-sloop HMS Gannet, which sailed first into the Mediterranean before crossing the Atlantic for four years’ service in North America and the West Indies.

[6] Two other future Franklin expedition men, Charles Hamilton Osmer and James Walter Fairholme, served aboard Gannet at the same time as Peglar.

His service was unremarkable, and Sir John Hill (who was later in charge of the Deptford Victualling Yard when the Franklin Expedition was fitted out) recorded his conduct as "indifferent.

Due to the activity there, Denman as captain of the Wanderer made treaties with local chiefs and expelled slave-traders before moving on to Sierra Leone where up to 200 slaves were emancipated.

[17] Two other Wanderer men joined after him: George Henry Hodgson (on the recommendation of Erebus commander James Fitzjames) and William Gibson, who had served as an ordinary seaman in both West Africa and China.

[19] In April 1848, Erebus and Terror were still beset by ice, and twenty-one men including Commander of the Expedition John Franklin and Lieutenant Graham Gore had died.

[2] Shortly after midnight on 25 May 1859, Francis Leopold McClintock, while investigating the Franklin Expedition on King William Island, came across a partly-exposed bleached human skeleton, face-down along a gravel ridge.

[20] It is the only human remains found within the 30 mile stretch between Washington Bay and Tulloch Point, and was never buried, indicating they may have been a solitary straggler who was separated from the main party, possibly by a sudden blizzard, a weather event known to occur on King William Island.

The skeleton was believed to not have been refound[20] until 2022, when Douglas Stenton identified that accounts and maps had geographic errors, and that the site had been found and excavated in 1973 by members of the 1st Battalion, Royal Canadian Regiment, CFB London, and the Defence and Civil Institute of Environmental Medicine.

The metatarsal is regarded as being from the remains exhumed in 1973 and DNA analyses provided mitochondrial and Y-chromosome haplogroups indicating a male of European ancestry, and the buttons are consistent with those found by earlier searchers.

[27] The writings with the skeleton included a mention of "Cumanar," referring to Cumaná, Venezuela, a city that Peglar and Armitage both visited from late 1834 through January 1835 while aboard Gannet.

[32] Subordinate officer's steward William Gibson had a longer and more recent connection to Peglar, as they served together between January 1840 and June 1844 aboard Wanderer, working together in operations against pirates and slavers.

These represent a eulogy, as the opening line is from the Service for the Burial of the Dead in the Book of Common Prayer, a text with which all Royal Navy seamen would have been expected to be familiar with.

Other lines including "The Dyer was and whare Traffalegar [sic]" circumstantially suggest that the burial service being transcribed was Franklin's, as he was the only expedition member who was also a veteran of the Battle of Trafalgar.

[35] Other references to events occurring during the expedition are also within the text: a drawing of "Lid Bay," a place encountered by the expedition and named on account of its eye-like shape, references to "new boots," "hard ground to heave" (either grave-digging or sledge-hauling) and the phrase "Terror Camp is clear," but due to the poor legibility of the documents the full context is missing, and most of the sentences remain unreadable without advanced forensic techniques.

Heathfield became a member of the Royal Geographical Society in 1863, and was acquainted with Roderick Murchison, indicating some connexion to Arctic exploration, but there are no known ties between him and Peglar or Armitage.