Born in London, the third youngest of ten siblings, Jacob was educated at Dulwich College in South London, England. His career almost ended before it began. He enlisted in the Field Artillery to serve in World War I when he was 19. The vagaries of war pushed him into the infantry, in the trenches in the front line. He was taken prisoner of war in 1917, and was one of only 60 men in his battalion of 800 to survive. He amused himself and his fellow POWs by forming a small prison camp "orchestra" of any instruments they could muster, and arranging music for it. At this period he received the news that his brother Anstey, who had enlisted with him, had died in the Somme, and this he commemorated some years later in his 1st Symphony.
After being released he spent a year studying journalism, but left to study composition, theory, and conducting at the Royal College of Music. Because of his cleft palate and a childhood hand injury, his instrumental abilities were limited; he studied piano but never had a performing career. Jacob's first major successful piece was composed during his student years: the William Byrd Suite for orchestra, after a collection of pieces for the virginals. It is better-known in a later arrangement for symphonic band. While a student Jacob was asked by Ralph Vaughan Williams to arrange the latter's English Folk Song Suite for full orchestra.
He taught at the Royal College of Music from 1924 until his retirement in 1966. Malcolm Arnold, Frank Bury, Ruth Gipps, Imogen Holst, Cyril Smith, Philip Cannon and Robert Turner were among his students. Jacob became a Fellow of the Royal College in 1946, and throughout his career often wrote pieces for particular students and faculties.
In the 1930s Jacob, along with several other young composers, wrote for the Sadlers Wells Ballet Company. His one original ballet, Uncle Remus, was written for them, but most of his contributions were arrangements of established works, such as Les Sylphides, for which his version remains in use, though the rival orchestration by Roy Douglas has been more often recorded for disc. Later ballet scores arranged by Jacob include Mam'zelle Angot, (based on Charles Lecocq's music, which remains in the repertoire of the Royal Ballet) and, in 1958, London Morning, composed for the London Festival Ballet by Noel Coward and orchestrated by Jacob.
Jacob also contributed light music to a morale-boosting comedy radio show during World War II, which earned him the disdain of the musical elitists and the appreciation of the public. He also wrote music for several propaganda films.
In the 1940s he was commissioned, on the recommendation of Sir Adrian Boult to orchestrate Elgar's Organ Sonata. A recording of this version was made in 1988 by EMI.
The height of his renown was in the 1950s, during which his Music for a Festival was used for the 1951 Festival of Britain, and his trumpet-heavy fanfare arrangement of the National Anthem was used for the 1953 coronation of Queen Elizabeth II.
After his retirement from the Royal College in 1966, he continued to support himself by composing, often on commission. He describes many of the works as "unpretentious little pieces", though some of his most important works were published during this time, including his Concerto for Timpani and Wind Band in 1984.
Jacob married twice, once in 1924 to Sidney Gray, who died in 1958, and again a year after her death, to her niece Margaret Gray, in 1959. He had two children by Margaret, who was 42 years his junior. He died in Saffron Walden in 1984.
There is a 1959 BBC documentary about his life, Gordon Jacob, directed by Ken Russell, as well as a 1995 book by Eric Wetherell entitled Gordon Jacob: a Centenary Biography.
Jacob was one of the most musically conservative of his generation of composers. Though he studied with Vaughan Williams and Stanford at the Royal College, Jacob preferred the more austere Baroque and Classical models to the Romanticism of his peers, and stuck to this aesthetic even in the face of the trends toward atonality and serialism.
This conservatism later caused his works to fall out of fashion when the 1960s establishment favoured the avant-garde. Jacob held the movement in little regard, saying "I personally feel repelled by the intellectual snobbery of some progressive artists... the day that melody is discarded altogether, you may as well pack up music...". Not all contemporary listeners found his music too conservative or melodic: "Foul music by Gordon Jacob just over, in which the pianist stamped on, kicked, butted, thumped and finally threw out of the window the long-suffering piano." Lyttelton/Hart-Davis Letters, 23 January 1958
He was a skilful writer for winds, and a good deal of his present-day reputation is because he embraced the wind band, which had begun coming into its own as a concert ensemble. Additionally, he published solo and chamber literature at various levels of difficulty for nearly all the wind instruments, many of which are now standard items in the pedagogical and performing repertoires.
Jacob was prolific, publishing over 700 pieces of music in addition to his four books and numerous essays on music.