Cédric Herrou is facing up to five years in prison and 30,000 euros in fines for helping 200 migrants, mainly from Eritrea and Sudan, cross into France from the Italian city of Ventimiglia.
Herrou allows the migrants to live under makeshift tents behind his small home.
He will go on trial Wednesday in a Nice criminal court. Activists plan to hold a rally nearby.
The French site 20 Minutes has video of Herrou and his migrant dependents.