While his music remains obscure, he was important as the teacher of several of the composers of the golden age of Portuguese polyphony, including Duarte Lobo and Manuel Cardoso.
He was born in Lisbon, and studied music with Cosme Delgado in Évora as a youth.
Later he was appointed mestre de capela at the cathedral in Portalegre, but returned to Évora to receive a bachelor's degree in 1575.
While Mendes was evidently a prolific composer, his works are only extant in manuscript.
He was famous in the 16th century, and his music traveled to Spain as well as Mexico, where he was highly regarded.