William was born and raised in Green Bay, WI Inspired and learned magic from tricks bought by his father, who owned Green Bay Canning Co.
He moved to Pasadena, CA in 1922 to be a criminal attorney. He later gave up his practice to become a full time magician at resort hotels and other venues.
William contributed a number of routines, both in his name and a pen name, J. Mark Hall, to SPHINX in the early 20s. One idea of his was called "Finger Prints" which would later become the "Out to Lunch" principle.
In 1936 William founded GENII Magazine along with his wife Gerri, who was a magician in her own right. The magazine is the longest running independent magazine devoted to magic and magicians in the history of the art. Richard Kaufman is the currently publisher.
In 1939, he toured the USA with a full evening magic stage show with his wife and their two sons, Bill, Jr. and Milt.
1942-1947 purchased and operated Thayer Magic company.
The Academy of Magical Arts was created by William in 1952, in the pages of Genii. For many years he dreamed of building a meeting place for magicians and a home for the Academy. He died a year later, of a cerebral hemmorage due to alcoholism, never realizing his dream. In 1963, Milt and Bill took took their fathers idea and opened the Magic Castle in Hollywood, CA.
William wrote and published manuscripts, mostly on mentalism. His son Bill, Jr. put some of the manuscripts together to create The Mental Mysteries of William Larsen, Sr. (1977)