Jacob was born in London on July 5, 1895, the youngest of 10 children. Educated at Dulwich College, he served in the army during World War I and was lucky to return home: he was one of only 60 survivors of the 800 soldiers in his battalion.
Jacob received his musical training at the Royal College of Music under Vaughan Williams, Stanford, and other notables. Jacob himself joined the faculty there in 1924 and held the post until 1966. He wrote music and arrangements for the Sadlers Wells Ballet Company in the 1930s, and in the next decade turned out patriotic pieces and film scores for the war effort.
Jacob's Music for a Festival was an immediate hit at the 1951 Festival of Britain. The 1959 Ken Russell-directed BBC TV documentary about the life of Jacob divulged both the composer's conservative artistry and his importance, then at its peak, in England. The year of the film's release Jacob remarried (his first wife died childless in 1958), and fathered two children to his second wife. After his 1966 retirement from the RCM Jacob remained active, though his reputation was in decline owing to the more fashionable works by serial and other progressive-minded composers. Jacob's 1984 Concerto for Timpani and Wind Band is among his more important late works.