Fitzsimmons was born the youngest child of two blind parents, and was raised in Pittsburgh, Pennsylvania. He is said to have developed his multiple instrument abilities from his mother and father, both of whom were recreational musicians. His childhood home even housed a fully functional pipe organ, said to have been built by hand by his father. He was taught the piano and trombone during elementary school, and began teaching himself guitar during his Jr. High years. He is also proficient at the banjo, melodica, ukulele, and mandolin, and is known for mixing folk music with electronica in some of his production. In addition to performance abilities, Fitzsimmons is credited as the engineer and producer of all his recorded music. He is often compared to contemporaries Iron & Wine, Sufjan Stevens, and the late Elliott Smith.

William's career in music came only after completing a Master's Degree in counseling, and working as a mental health therapist. Prior to his graduate studies, Fitzsimmons worked with the mentally ill for several years. It was during a summer break in the midst of graduate school that Fitzsimmons recorded a collection of songs on home recording equipment which would subsequently become his debut album.

Fitzsimmons' writing often includes reference to personal and family subject matter. His latest album, Goodnight, is said to have been based largely on his own parents' divorce during his adolescence.

Fitzsimmons' music became noticed largely through Myspace, the popular, internet social networking site, and eventual touring with Ingrid Michaelson and Cary Brothers.

He currently lives in Illinois and is said to be writing for a new album and planning future tour dates.

• Until When We Are Ghosts (2005)
• Goodnight (2006)
• The Sparrow and the Crow (2008)