Willard was born on the 5th of June 1877, in Maitland, Canada, and it is known that at least he and his younger brother Harry moved to the US and enlisted in the US Navy in Massachusetts. He deployed to Cuba in support of the Spanish-American War and his actions as a Seaman would later earn him the Medal of Honor. The citation reads:

On board the U.S.S. Nashville during the operation of cutting the cable leading from Cienfuegos, Cuba, 11 May 1898. Facing the heavy fire of the enemy, Miller displayed extraordinary bravery and coolness throughout this action.

Willard and Harry both received the Medal of Honor on the 7th of July 1899, and they are one of eight pairs of brothers to both be awarded the Medal of Honor. Willard exited the Navy seven years later and went on to work for the US Lighthouse Service. Not much else is recorded about his life and I found no record of a wife or children. Willard Dwight Miller died on the 19th of February 1959, at the age of 81, in Salt Lake City, Utah. He is buried in Arlington National Cemetery: Section 46, Grave 15.