David John White was born on 2nd February 1940 in Finchley, North London. His father, Arthur, was a porter at Billingsgate Fish Market and his mother, Olwen, a charlady, was employed to clean houses. David had an elder brother, also called Arthur, and his sister, June, came along later. The family lived in a modest terraced house and David went to school nearby. It was at school, at the age of 14, that the acting bug first bit young David White, although he was, at first, something of a reluctant performer. He was drafted into the play (a Civil War drama - Wayside War), to play a Cavalier, when one of his classmates was forced to withdraw due to contracting measles. David had up to that point considered acting to be something that only girls did, and really didn't want to be involved at all. However, to his surprise he discovered that he actually loved every minute of it and as a direct result of this play, David joined an amateur dramatics society.

Leaving school at 15 David pursued his parent's wishes to get himself a trade by working in a garage as a trainee mechanic. However, after a year he decided that working on cars was not for him and he switched courses to become an electrician. He continued to tread the boards in a number of amateur productions hoping to follow his brother Arthur into professional acting. For the time being though, David continued to learn his "trade" and by the time he'd reached his twenties he had set up a business with a friend, Bob Bevil, called B & W Instillations.

In March 1965, a golden opportunity presented itself when his elder brother, Arthur, pulled out of a Noël Coward play called South Sea Bubble in favour of a television role in Z Cars. Arthur recommended that David take his place in South Sea Bubble, and after seeing him in an amateur production, the director offered him the part, which earned him £9 per week. David made his professional acting debut in the play for Bromley Rep on 5th April 1965. On turning professional David decided to change his surname to Jason, as there was already a David White in the acting world. After his professional debut other work followed, but acting jobs were few and far between. David returned to Bromley Rep on a one-year contract where he played various roles, usually comedy ones, which directors had noticed he had a flair for. It was while at Bromley Rep that David first met Lennard Pearce, who would later play Granddad to David's Del Boy in Only Fools and Horses. They were both appearing in an eighteenth century comedy called The Rivals, and despite getting on well would not meet again for another fifteen years.

After Bromley Rep David continued his stage career and worked with such stars as Bob Monkhouse and Dick Emery during summer seasons. In 1967 he made his television debut appearing with Michael Palin, Eric Idle and Terry Jones in the children's programme Do Not Adjust Your Set, a forerunner to Monty Python's Flying Circus. One of the characters that David played became a firm favourite in the show, that of Captain Fantastic, an ordinary looking "superhero" who was pitted against his arch enemy Mrs Black (the most evil woman in the world) as played by Denise Coffey. DNAYS had a very successful run on ITV and ended in 1969, but it was during this run that David missed out on what eventually became one of the most famous roles in British television history; that of Corporal Jack Jones in the new Jimmy Perry and David Croft BBC comedy Dads Army.

The original choice for the part was Clive Dunn, but unfortunately Clive was appearing in the Spike Milligan Show at the time and was not available. David Croft had worked with David Jason before when the former had produced a comedy series for the BBC called Hugh and I, which starred Hugh Lloyd and Terry Scott as two friends who lived together in south London. Although Jason had only played some minor parts in the series, Croft had been very impressed with the youngster and knew that he had the ability to play a man much older than his own age. After reading for the part David was told that it was his, only to be told later (about three hours later, in fact), that Clive Dunn was suddenly now available and could perform the role after all.

When Do Not Adjust Your Set ended in 1969 and David landed a small role playing a gardener in the ITV soap Crossroads. His next television job gave him his biggest break. He again played a gardener, but this time his character, Dithers, was one hundred years old! Humphrey Barclay, the man behind DNAYS, was producing a new series of comedies for Ronnie Barker called Hark at Barker, and was casting for an actor who could play this decrepit old gardener whilst being young enough to perform the numerous stunts that were going to be asked of him. Barker and Jason hit it off immediately. Josephine Tewson, the actress that played Bates, secretary to Barker's Lord Rustless in the series, remembers what Barker had to say about David Jason in 1969. "I can remember Ronnie saying then 'he's going to give us work when we get old and crotchety.' He could see the potential David had and how good he was."

In 1973 Ronnie Barker made a series of seven one-off comedy shows and David was offered a part in one of them called Open All Hours in which he played Granville, the nephew of the miserly Yorkshire shopkeeper, Arkwright. The series was not an instant success when shown on BBC2 but on its repeat run on BBC1 it became a big hit. One of the highlights of the series was the two perfectly pitched performances of two top flight comedy actors whose rapport was in total synch not only with each other, but also material of the very highest quality.

Another of the one-offs was called Prisoner and Escort, which was also made into a series -re-named Porridge. David appeared in three episodes of Porridge playing an elderly prisoner called Blanco Webb. In 1974 David had got his first television-starring role in The Top Secret Life of Edgar Briggs and in 1976 (the year that the full series of Open All Hours was made) he starred as Shorty Mepstead in Lucky Feller. In 1978 he played Peter Barnes in A Sharp Intake of Breath.