He attended the Bonifacius School in Utrecht. He studied drama and (briefly) law.
In 1955 Van Hemert adapted William Inge"s Come Back, Little Sheba for Dutch television Two years later, in 1957, he wrote the lyrics for the winning song at the 1957 Eurovision Song Contest, "Net als toen", performed by Corry Brokken. Van Hemert also wrote the lyrics for the Dutch entry the following year when the contest was staged in London (as The Netherlands had hosted the 1958 Edition).
The song was called "Wat een geluk" and was performed by Rudi Carrell.
His most famous song may be "Zuiderzeeballade", or "Ballad of the Zuiderzee", a song from 1962 that ranked ninth in the top 100 of most popular Dutch songs from the twentieth century. Willy van Hemert died, aged 81, in Hechtel.