[2] Van Deventer was born in Leiden, were his father ran a wine store.
After secondary school he started working as sales agent for a flower factory and married Emmy van Deventer in 1936.
[2] In 1936 Just and Emmy Van Deventer moved to Amsterdam-Zuid, where they lived among artists as Nel Houtman, Fred Carasso, and Jan Wolkers.
After the war he started the ceramic factory "De Marmot," next to the studio of John Rädecker.
From 1950 to 1956 he lectured at the Free Academy in The Hague, and from 1953 until his death in 1957 at the AKV St. Joost in Breda.