William Floyd Millet lettered in basketball, football, and track while earning a degree at Brigham Young University. He attended Gila Junior College (now Western Arizona College).
He began his coaching career at Davis High School in Kaysville, Utah, and was head coach in football and baseball for three years. He was also assistant coach in basketball. In 1937 he became an assistant coach at BYU from 1937 to 1941 before becoming the head coach for the 1942 season. (BYU did not play from 1943 to 1945 due to World War II.) Millet was also BYU's athletic director from 1963 to 1970. Millet was also the head basketball coach from 1941 to 1949.
He was inducted into the BYU Athletic Hall of Fame in 1976.
Millet was born on October 17, 1911, in Mesa, Arizona. He passed away on June 17, 2000. He and his wife, Vera, were both members of The Church of Jesus Christ of Latter-day Saints. He served on the YMMIA general board. They were the parents of four children.