Subsequently, he pursued advanced studies in the conservatory of music in Basel, Switzerland, honing his skills as an accomplished violinist.

The year 1943 marked a significant milestone when he wrote songs for the weekly Assyrian program broadcast on national radio.

Additionally, Daniel organized choirs, plays, concerts, and taught classes in the Assyrian language and literature, fostering cultural growth.

During his Chicago years (1952–1979), he published the second volume of Kateeny the Great; his music collection titled William Daniel's Creations; Assyrians of Today, Their Problems and a Solution; and the bilingual play Kismat.

His students posthumously honored him in 1992 by publishing his previously unpublished poems in Assyrian and English in an illustrated book titled Tapestry.