After leaving LSE, Mackworth spent much of the next two decades traveling. She married Leon Donckier de Donceel, a Belgian lawyer, at the age of 22 after meeting him in a Swiss sanitarium. The couple had one daughter before he died three years into their marriage. She spent time in Hungary and Germany, witnessing the burning of the Reichstag in 1933, before settling in Paris in 1936. Forced to flee Paris in 1940, she worked briefly for the Free Frenchin London during the war, in addition to giving lectures to the army and writing for Cyril Connolly's literary magazine Horizon. While in London she became familiar with a number of contemporary writers, including T.S. Eliot, who admired an early book of hers detailing her recent flight from France. In one notable incident during this time, Dylan Thomas' wife, Caitlin, stubbed a cigarette out on Mackworth's hand, on the grounds that Mackworth was acting too intimately with her husband at a party.