Lay was the son of painter Oliver Ingraham Lay. He entered the Columbia University School of Architecture, New York, in 1896, and following graduation in 1900, went to the Harvard University School of Landscape Architecture, Cambridge, Massachusetts, for two further years of study, receiving a Bachelor of Science degree in Arts Topiaria in 1902. He established his practice in New York, and became one of the most widely respected landscape architects in the country; he also enjoyed considerable standing as a painter and etcher.
In addition to his extensive work designing gardens and landscape planning for private clients, Lay was responsible for many public parks, notably for the city of New York. the landscape designs for the Jacob Riis, Sheepshead Bay, and St. Nicholas city housing projects, and the 1912 design for Fort Tryon Park, were among his New York projects. He served as a consultant architect for the 1939 New York World's Fair, and during World War II as a consultant to the United States Navy worked on landscaping airfields. In 1948 Lay founded and directed the Housatonic Valley (Connecticut) Planning Association dedicated to developing recreatonal areas on the River.
Lay's influence on landscape design was especially extended by his writings in the field. He was a founder of the quarterly magazine Landscape Architecture, was its editor and manager from 1910 to 1921. Among the books he authored were A Garden Book for Autumn and Winter, 1924, and The Freedom of the City, 1926.
He was a fellow of American Society of Landscape Architects and of the American Institute of Planners; and a member of New York Municipal Art Commission, American Institute of Architects, and Art Students League.
