Peter Warlock was born Philip Heseltine in the Savoy Hotel, the only son of a London solicitor. His father died when he was two, and Heseltine was raised by his mother. He was educated in the English public schools, and was encouraged in his passion for music by a teacher at Eton, Colin Taylor. Outside of that, he had little or no significant musical training. In 1908, Heseltine discovered the music of Frederick Delius and was enraptured by his work; upon meeting Delius in 1911, a lifelong friendship ensued. Heseltine entered Oxford in 1913, but soon dropped out, relocating to London to work as music critic for the Daily Mail. With the outbreak of war, Heseltine was deemed unfit for military duty. In 1916 adopted the pen name "Peter Warlock" amid a host of others used in his criticism. When he began to compose seriously around 1918, this was the pseudonym that Heseltine favored for his original work.
In 1918, Warlock and composer Cecil Gray undertook publication of The Sackbut, a periodical dedicated to informed and lively discussion of the contemporary music world. Warlock held this post until the magazine was absorbed into the house of publisher J.C. Curwen in 1921. Warlock also turned his attention to English music of past eras, particularly that of the Elizabethan age. He would edit a great deal of this "ancient" music for modern publication, and Warlock's editions are of such a high standard that generations of subsequent research have failed to unseat many of them. In 1923, he composed his song cycle to poems of Yeats, The Curlew, which represented Britain in the 1924 ISCM Festival in Salzburg. That same year, he scored three Christmas carols for the Bach Choir; this set contained the ethereal and mystic Balulalow, since becoming a choral staple of the Yuletide season. Warlock's Capriol Suite, his best known orchestral work, was completed in 1926. Another famous Christmas carol, Bethlehem Down, made its bow in The London Daily Telegraph's Christmas Eve edition of 1927. He published book length essays on Delius, Gesualdo, and Thomas Whythorne.
In early 1929, Thomas Beecham named Warlock editor of MILO (The Magazine of the Imperial League of Opera). Only three issues appeared before the magazine folded. Warlock fell into a deep depression, unable to find work and drinking heavily. On December 17, 1930, Warlock's landlady phoned her utility company as there was a strong smell of gas coming from Warlock's flat. Once inside, the police found Warlock dead from asphyxiation at the age of 36.
Warlock's main output consists of songs, written in a modern style, characterized by extroverted ebulliance on one hand and serene, transparent calm on the other. Critics who deal with Warlock sometimes attempt to present him as a kind of schizophrenic, transporting good qualities to "Heseltine" and bad to "Warlock." From reminiscences of his friends, it seems a more complex situation. Heseltine/Warlock was an alcoholic, a naughty limericks writer, and a sadist who often lashed out in the press against bad performances and the opinions of writers, particularly Edwin Newman, whose views offended him. Warlock's music was of its own special category; as conductor/composer Constant Lambert noted in 1938, "It would be an easy matter for me to write down the names of at least 30 of [Warlock's] songs which are flawless in inspiration and workmanship. It is no exaggeration to say that this achievement entitles him to be classed with Dowland, Mussorgsky, and Debussy as one of the greatest song writers that music has known."