In the late 1920s and early 1930s he published biographies of John Wilkes and Robert Emmet and his first novel, "No Epitaph" (1932), and worked as an editor for the "Encyclopædia Britannica". In 1932 he visited the Soviet Union with a Fabian delegation and contributed to the collection "Twelve Studies in Soviet Russia". Later in the 1930s he co-authored with his brother-in-law G. D. H. Cole "The Common People", a social history of Britain from the mid-18th century. Postgate edited the left-wing monthly "Fact" from 1937 to 1939, which featured a monograph on a different subject in each issue. "Fact" published material by several well-known left-wing writers, including Ernest Hemingway's reports on the Spanish Civil War, C. L. R. James' "A History of Negro Revolt" and Storm Jameson's essay "Documents". Postgate then edited the socialist weekly "Tribune" from early 1940 until the end of 1941. "Tribune" had previously been a pro-Soviet publication: however, the Soviet fellow travellers at "Tribune" were either dismissed, or, in Postgate's words "left soon after in dislike of me". Under Postgate's editorship, "Tribune" would express "critical support" for the Churchill government and condemn the Communist Party.