During the era of the Popular Front, Slesinger was a supporter of the American Communist Party. Her name was among those included on the letter denouncing the Dewey Commission's investigation of the Moscow Trials, and she also endorsed the CP-initiated call for the Third American Writers' Congress in 1939. However, like many other leftist intellectuals of the time, Slesinger grew disillusioned with the Soviet Union in the wake of the Hitler-Stalin Pact of 1939. Maxim Lieber served as her literary agent, 1933–1937 and in 1941.