The defender - who can also play in midfielder - has reportedly rejected a new contract with Marseille, leaving him open to join Everton.
The Frenchman will reportedly immediately join in first-team training but will play his football for Everton's U23 side.
“Niels is a young, talented player with good technical and physical skills," said Brands. “We have been following him for months.
“Hopefully he can learn a lot from Lucas Digne and Leighton Baines, as well as Carlo Ancelotti and David Unsworth, and follow the same pathway into the first team the likes of Dominic Calvert-Lewin and Mason Holgate have taken in recent years."