In the following years Muir became Vice-Principal of a teacher training college in London, but had to leave when, in 1919, she married the critic and poet, Edwin Muir. After their marriage, Edwin Muir was to become one of the central figures of the modern Scottish cultural renaissance.

During the 1920s and 30s the Muirs travelled extensively around Europe, living in Prague, as well as in Germany, Austria and Italy. Both were interested by developments in European literature at the time and, between 1930 and 1962, they translated more than forty novels, the best known of which are the works of the German writer Franz Kafka. Although the Muirs worked together, it is now acknowledged that Willa, a more able linguist, was probably the main translator in these projects, also translating many books herself, under the name of Agnes Neill Scott.

Willa Muir wrote only two novels, the first of which, Imagined Corners, was published in 1931 when she was in her forties. Like her second novel, Mrs Ritchie, which appeared two years later, it explores the conventions of small town Scottish life, such as the negative effects of Calvinism, and is particularly concerned with the limitations experienced by women in these settings. Muir also wrote two extended essays, Mrs Grundy in Scotland and Women in Scotland, both published in 1936, which examine the roles open to women in contemporary Scotland.

Having left Shetland in childhood, Muir sensed throughout her life that she lacked a place to which she really belonged - a sense of rootlessness which she shared with her husband, and which must have been heightened by their frequent travelling. After his death, she wrote a moving account of their life together entitled, Belonging: A Memoir (1968). She also wrote a study of oral poetry, Living with Ballads (1965), and several extended sociological essays in which (as in her novels) she turned her perceptive eye on Scotland and the feminist issues of the day.

While her collected writings are not extensive, her contribution to the modern Scottish Renaissance is nevertheless important, and it is recognised that she may well have written more had she not had to focus on making money from her translations, or poured her creative energies into encouraging the often troubled career of her more famous husband, Edwin, whom she outlived by some eleven years. She died on 22 May, 1970.