William Royall Tyler (October 17, 1910 – November 16, 2003) was a United States diplomat.

After college, Tyler spent five years working as an international banker in England and the United States.

In 1962, President of the United States John F. Kennedy nominated Tyler as Assistant Secretary of State for European Affairs, and, after Senate confirmation, Tyler held this office from September 2, 1962 until May 18, 1965.

Tyler left government service in 1969, becoming director of the Dumbarton Oaks Research Library and Collection, one of the world's foremost research libraries in the field of Byzantine studies.

He died at a nursing facility in Bristol, Vermont on November 16, 2003, after suffering from Alzheimer's and Parkinson's disease.