Warburg started his publishing career in 1922, as an apprentice at Routledge & Sons, where he came under the tutelage of William Swan Stallybrass, a man he regarded as "the greatest scholar-publisher of his day". After Stallybrass died in 1931 Warburg became increasingly dissatisfied with Routledge and in 1935 he was dismissed. Later that year he and Roger Senhouse purchased the publishing firm of Martin Secker, which had gone into receivership, and renamed it Secker & Warburg. The firm became renowned for its independent left-wing position, being both anti-fascist and anti-Communist, which put it at loggerheads with many intellectuals of the time. Among the books the firm published were C. L. R. James's "World Revolution", Reg Groves's "We Shall Rise Again", Boris Souvarine's "Stalin" and André Gide's "Back from the USSR". When George Orwell parted company with Victor Gollancz over publication of "The Road to Wigan Pier" it was to Secker & Warburg that he took his next book, "Homage to Catalonia". The firm published all of Orwell's books from then on, and he and Warburg became intimate friends. In 1940 Warburg introduced Orwell to another of his firm's authors, T. R. Fyvel and between the three of them they planned the creation of Searchlight Books.