Brunet was born in Badalona on 14 September 1872, son of the primary teacher Josep Brunet i Bassachs, native from the same town, and Joana Forroll i Codina, from Tiana. During his childhood showed interest in drawing and painting and had contact with Antoni Caba, a prestigious painter and former director from Barcelona Arts and Crafts School who was also a friend of his father, to whom he promised to protect and help Llorenç study art.
