Answer by taking a quote from the following article:

Sir George Henry Martin  (3 January 1926 - 8 March 2016) was an English record producer, arranger, composer, conductor, audio engineer, and musician. He was referred to as the "Fifth Beatle", including by Paul McCartney, in reference to his extensive involvement on each of the Beatles' original albums. Martin produced 30 number-one hit singles in the United Kingdom and 23 number-one hits in the United States. Martin produced comedy and novelty records in the early 1950s, working with Peter Sellers, Spike Milligan, and Bernard Cribbins, among others.

Martin was born in Highbury, London. When he was six, Martin's family acquired a piano that sparked his interest in music. At eight years of age, Martin persuaded his parents, Henry and Betha Beatrice (nee Simpson) Martin, that he should take piano lessons, but those ended after only eight lessons because of a disagreement between his mother and the teacher.  As a child, he attended several schools, including a "convent school in Holloway", St Joseph's School (Highgate), and at St Ignatius' College (Stamford Hill), where he had won a scholarship. When WWII broke out, and St. Ignatius College students were evacuated to Welwyn Garden City, his family left London, and he was enrolled at Bromley Grammar School.  I remember well the very first time I heard a symphony orchestra. I was just in my teens when Sir Adrian Boult brought the BBC Symphony Orchestra to my school for a public concert. It was absolutely magical. Hearing such glorious sounds I found it difficult to connect them with ninety men and women blowing into brass and wooden instruments or scraping away at strings with horsehair bows.  Despite Martin's continued interest in music, and "fantasies about being the next Rachmaninov", he did not initially choose music as a career. He worked briefly as a quantity surveyor, and later for the War Office as a Temporary Clerk (Grade Three), which meant filing paperwork and making tea.  In 1943, when he was 17, he joined the Fleet Air Arm of the Royal Navy and became an aerial observer and a commissioned officer. The war ended before Martin was involved in any combat, and he left the service in 1947. Encouraged by Sidney Harrison (a member of the Committee for the Promotion of New Music) Martin used his veteran's grant to attend the Guildhall School of Music and Drama from 1947 to 1950, where he studied piano and oboe, and was interested in the music of Rachmaninoff and Ravel, as well as Cole Porter. Martin's oboe teacher was Margaret Eliot (the mother of Jane Asher, who would later become involved with Paul McCartney). After that, Martin explained that he had just picked it up by himself. On 3 January 1948 - while still at the Academy - Martin married Sheena Chisholm, with whom he would have two children, Alexis and Gregory Paul Martin. He later married Judy Lockhart-Smith on 24 June 1966, and they also had two children, Lucie and Giles Martin.

what was his first work
He worked briefly as a quantity surveyor, and later for the War Office as a Temporary Clerk