Active in pacifist and social reform efforts, Malleson spent the remainder of her career traveling and writing. She released several novels and autobiographical accounts, including "In the north : autobiographical fragments in Norway, Sweden, Finland, 1936-1946" about her experiences in Scandinavia administering relief efforts in response to the Russo-Finnish War. Among her most notable releases is the 1933 novel "The Coming Back". Though she denied the suggestion, it is understood as a roman à clef regarding Malleson's relationship with philosopher and political activist Bertrand Russell, with whom she shared an interest in pacifism. Friends until Russell's death, the pair were romantically involved from 1916 to 1920, during Malleson's mutually open marriage to actor Miles Malleson.