During the 1930s, Markham's artistic career began to gain momentum, regularly winning prizes for her lithographic work. In 1934, Markham organized her first solo exhibition in Ogunquit, Maine, featuring prints, murals and lithographs. Markham created works of social realism depicting street beggars, musicians, actors and scenes from department stores. In recognition of her work, Markham received the prestigious Mary S. Collins Prize at the Philadelphia Print Club's annual exhibition the following year for her lithograph "Elin and Maria" (1934). Markham sold work to the Whitney Museum of American Art, the Library of Congress and the Metropolitan Museum of Art. From 1935 to 1937, she worked in the Graphic Arts Division for the Federal Arts Project, a New Deal program designed to provide employment for artists during the Depression. The "Hall of Inventions" at the 1939 World's Fair in New York included 40 dioramas by Markham. During World War II she created propaganda satirizing the Nazis and promoting patriotism at home. In 1946 Markham and Gaither moved to an old farmhouse in Halifax, Vermont. Markham stopped making prints after moving to her remote Vermont farm, but continued to work in more accessible mediums such as painting, drawing and ceramics. She was a member of the Southern Vermont Artists Association and participated in their annual exhibitions in Manchester. Over the next twenty years she sold her designs to a postcard company, American Arts, Inc., and had her prints published in prestigious publications. Markham also worked as an illustrator for Children’s books during this time.