Large was born in Oxfordshire, the first child of Joseph Large and his wife Emily (née Pratley). He had a sister, Janet, who was nine years his junior. In 1939, the family moved to a cottage two miles outside the village of Guiting Power in the Gloucestershire Cotswolds. As a child his father taught him how to shoot game; he later said of this experience, "little did I realise I would spend a lot of time, many years later [in the SAS], being trained in exactly that type of instinctive shooting."

Growing up during the Second World War, and watching British and American soldiers on field exercises in the Cotswold Hills, Large later said that he had always wanted to be a soldier. He also joined the Army Cadet Force.

Large joined the Army at the age of fifteen as a "band boy". A lack of vacancies meant that he was unable to join his county regiment, The Glosters, so he instead joined the Wiltshire Regiment. After spending five years in England, Germany and Hong Kong, he requested a transfer to the Gloucestershire Regiment and then volunteered to fight in the Korean War. After a combat training course in Japan, Large was deployed to the front line.

Korean War

In March 1951, along with thirty other Glosters, Large was sent to B Company's position in the low hills above the Imjin River. The Glosters, as part of the 29th Brigade, were defending routes through the valley that could potentially be used by the Chinese in a southbound offensive towards Seoul. On 22 April 1951, they engaged with Chinese troops in the Battle of Imjin. By the morning of 24 April, B Company had fought off seven assaults before they were able to rejoin the remainder of their battalion on what became known as Gloster Hill. By this time the battalion was low on ammunition and cut off from the British lines. Large himself was shot in the left shoulder and, along with most of the remaining Glosters, was forced to surrender.

After a ten-day forced march north, and having received only basic medical attention, Large arrived at a prison camp outside Chongsung. He spent the next two years in the camp and celebrated his 21st birthday there. Throughout this time he had two bullets and at least eighteen pieces of shrapnel embedded in his body. To help him cope with the chronic pain of his untreated injuries, he was introduced to marijuana (which grew wild in the area) by an American POW. Although he found it to be a very effective painkiller, he was rather alarmed by its psychoactive effects and therefore tried to limit his use of the drug. During his incarceration Large, like many of his fellow prisoners, also suffered from beri-beri and dysentery.

In March 1953, he was operated on by a Chinese doctor and a tracer round was removed from his ribs. This medical attention was in fact preliminary to his being released as part of a prisoner exchange. Having weighed in March 1951, he had dropped to by the time of his release. He also still had very limited movement in his left arm and was later told that if he had been treated by a British doctor at the time of his injury he would most likely have had his arm amputated.

Large was one of a batch of 22 exchanged British POWs whose release and subsequent return to Britain became front-page news: The Guardian newspaper reported that the group had been unaware of the death of King George VI (which had occurred over a year earlier) until after their release, but that they were now looking forward to the coronation of Queen Elizabeth II.

For its defence of Gloster Hill in the Battle of Imjin, the 1st Battalion, Gloucestershire Regiment was awarded the Presidential Unit Citation. The citation is conferred on units of the armed forces of the United States and of allied nations for extraordinary heroism in action against an armed enemy.

After returning to the UK, Large was offered a discharge on medical grounds, which he declined. He went on to serve briefly in the quartermaster's stores, as an instructor, and in the regimental police. Throughout this time he worked on regaining his fitness and rehabilitating his arm.

Special Air Service

In 1957, wanting to escape the "stupidities of drill" and the "bullshit" of the regular Army, Large volunteered for the SAS and successfully completed the selection course; however, almost immediately afterwards he crashed his BSA motorbike. Having injured his ankle in the crash, he had to repeat selection ... this time with one boot two sizes larger than the other in order to accommodate the bandages and swelling. He went on to serve with 22 SAS in Malaya, Oman, Borneo and Aden.

Large's first operation with the SAS was in Malaya, hunting the communist guerrillas engaged in the Malayan Emergency uprising. By the time of Large's involvement there was little communist activity and, despite months of jungle patrols and encounters with leeches, scorpions, civet cats and tigers, he never had any contact with MRLA guerrillas.

While suppressing a rebellion in Oman in 1958, Large infamously lost his temper with a recalcitrant donkey. Recalling the incident in a 2003 interview, he said:

Several weeks later, in January 1959, Large was part of the 'A' and 'D' Squadron assault on the Jebel Akhdar. This entailed a overnight ascent of the south side of the jebel, with each soldier carrying of kit. Having completed this climb the SAS were able to surprise and defeat the rebels, who had previously held the plateau as a virtually impregnable stronghold.

During the Indonesia—Malaysia confrontation in Borneo, Large was involved in Claret operations. As the leader of a four-man SAS patrol, he spent up to two weeks at a time hidden in the jungle on deniable incursions into Indonesia, performing reconnaissance or ambushing Indonesian forces. For his service in Borneo, he received a mention in despatches.

Parachuting was an important part of SAS training and operations, but it was not an experience that Large enjoyed. His considerable bulk meant that he descended far too quickly to have any chance of a comfortable landing, added to which he suffered from a fear of heights. Despite this, he eventually qualified as a parachute instructor, although the footnote on his course report read, "not suited to parachuting ... either in size or inclination."

Large spent the final years of his 27-year Army career as an instructor with 23 SAS, one of the SAS's two reserve regiments.

He wrote two books about his time in the Army: One Man's SAS and One Man's War in Korea. A third book, Soldier Against the Odds: From Korean War to SAS, consisted of revised versions of his first two books together with some additional material. Andy McNab has said that "[Large's first two books] were recommended reading for Regiment candidates. He was instrumental in setting the template for future members of the Regiment."

In his book SAS Heroes: Remarkable Soldiers, Extraordinary Men, former SAS soldier Pete Scholey describes Large as "simply the finest soldier [I] had ever met ... an inspiration to those around him ... with an admirable sense of fair play."

Andy McNab, who joined the SAS eleven years after Large's departure, has written about Large's enduring impact on the Regiment:

Before leaving for Hong Kong with the Wiltshire Regiment, Large had met Ann, who was working as a nanny at the regiment's depot in Devizes. She wrote to him five times a week during his captivity in Chongsung, although only ninety of these letters were actually delivered to Large. They eventually married in 1955 and afterwards lived in an Army rental property on the top floor of a farmhouse in Longford, on the outskirts of Gloucester. In 1960 they moved with the Regiment to Hereford, where they had two children, Andy and Donna.

After leaving the Army Large worked in the UK and the Middle East. Having earned a Heavy Goods Vehicle driving licence and a Qualified Testing Officer's certificate during his time in the Army, he spent the last fourteen years of his working life as a driving instructor.

In his seventies, Large, along with Pete Scholey, returned to the Borneo jungle as part of a 2003 Channel 4 documentary about the history of the SAS, taking the camera crew to the exact spot on the bank of the Sungei Koemba River where his patrol had successfully ambushed an Indonesian Army river boat in 1965.

Having been ill with leukaemia for three years, he died aged 76 at St Michael's Hospice, Hereford. His funeral was held on 1 November 2006 at St Martin's Church in Hereford.