Willem Smalt was a Dutch pianist and music educator. He was born in Rotterdam on 23 April 1888, the son of Anna Catharina Koch and the writer and journalist Willem Smalt. His grandfather, Johannes Reinier Smalt, promoted classical music in Rotterdam.
Smalt studied at the Cologne Conservatory, where he is also said to have taught. In 1917, he was appointed piano teacher at the music school of the Society for the Promotion of Music, led by Ulfert Schults. From 1942, he served as principal piano teacher at the Amsterdam Conservatory.
In 1920, he married Jeannette ten Noever de Brauw. They reportedly had five children, including Jan Smalt, who also became a musician.
Smalt died in Amsterdam on 4 April 1950. He was buried at Buitenveldert Cemetery.