Daniel Urban Kiley (September 2, 1912 – February 21, 2004) was an American landscape architect who worked in the modern style. Kiley designed over one thousand landscape projects including Gateway Arch National Park in St. Louis.

Kiley was born in the neighborhood of Roxbury in Boston, where his father was a construction manager. In 1930, Kiley graduated from Jamaica Plain High School. Two years later, he began a four-year apprenticeship with landscape architect Warren H. Manning, working without pay for the first year, during which he learned the fundamentals of the field and developed an interest in the role of plants in design. From 1936 to 1938, Kiley was a special student in the design program at Harvard University, now the Graduate School of Design, while continuing work with Manning. Among his classmates were Garrett Eckbo and James C. Rose, who also became influential landscape architects. After two years, upon Manning's death and the dissolution of his practice, Kiley left Harvard without graduating. He worked briefly for the National Park Service in Concord, New Hampshire, and later the United States Housing Authority, where he met architect Louis Kahn. On Kahn's advice, Kiley left the authority in 1940 to become a licensed practicing architect.

From 1943 to 1945, Kiley served in the United States Army as Captain in the Presentation Branch of the Office of Strategic Services, becoming its director after architect Eero Saarinen stepped down. At the end of World War II, Kiley designed the courtroom where the Nuremberg Trials were held. While in Europe, he visited the Château de Villandry and the Palace of Versailles, as well as the work of André Le Nôtre, whose formality and geometric layout shaped his later classical modernist style.

Following the war, Kiley found himself as one of the only modern landscape architects in the postwar building boom. In California, his colleagues Eckbo, Thomas Church, and others were also developing and practicing in the modernist style. Kiley reestablished his practice in Franconia, New Hampshire, and later moved to Charlotte, Vermont. In 1947, in collaboration with Saarinen, Kiley entered and won the competition to design the Gateway Arch National Park (then known as the Jefferson National Expansion Memorial), a high-profile project that launched his career.

Throughout Kiley's practice, he hired such designers as Cheryl Barton, Miho Mazereeuw, Kevin Roche, Harry Turbott, and Peter Walker.

In 2000, the actor Paul Hopkins portrayed Kiley in the miniseries Nuremberg, featuring Alec Baldwin.

In 2013, The Cultural Landscape Foundation organized a traveling exhibition titled The Landscape Architecture Legacy of Dan Kiley, which featured over forty newly commissioned photographs of Kiley's projects.

The Harvard University Graduate School of Design has an endowed fellowship in his name: the Daniel Urban Kiley Teaching Fellowship in Landscape Architecture. There is also an endowed lecture series called the Daniel Urban Kiley Lecture, which has been delivered by such designers as Julie Bargmann and James Corner.