During the First World War, her pacifist opinions brought her into contact with Bertrand Russell. The pair met in 1916 at a trial for Clifford Allen, then, chairman of the No-Conscription Fellowship. Having mutually agreed to an open marriage with her husband, Malleson and Russell carried on a relationship until 1920. During that time Russell struggled with how seriously Malleson took her career and her continued involvement with other men. Their affair eventually ended because she did not want children. The pair remained friends and corresponded until Russell's death in 1970. He didn't feel that acting made sufficient use of her talents and encouraged a writing career after she rejected his suggestion to become more politically active. It was Russell who submitted Malleson's first published short story, "The End", which was released in the September 1919 edition of the English Review under the pseudonym Christine Harte. Malleson eventually sold her letters from Russell and other mementos to McMaster University for inclusion in the Bertrand Russell Archives.