Herrou was given a four-month suspended prison sentence in August 2017 by an appeals court in Aix en Provence for helping about 150 migrants trying cross the Franco-Italian border.
The olive farmer was also convicted for sheltering some 50 Eritreans in a disused railway building.
The Vallée de Roya in the Alpes-Maritimes department of south-east France is an entry point for thousands of people who are trying to reach European countries after sailing across the Mediterranean.
The Aix-en-Provence court had in September of 2017 also sentenced the researcher Pierre-Alain Mannoni with a two-month suspended prison sentence for helping and transporting three Eritrean migrants in the same region.
His sentence was also overturned on Wednesday.
The humanitarian exception
According to an asylum-immigration article issued on 10 septembre 2018, helping foreigners is permitted by the law only if it is on a strictly humanitarian basis.
Herrou's victory came after his second appeal at a court in Lyon.
Herrou’s lawyer Patrice Spinosi, welcomed Wednesday's decision calling it a "humanitarian exception" and "a great victory" for his client.
"Lending a hand to a foreigner, as long as it's not done for gain, should not be punishable," the lawyer said after the first appeal hearing.
Prior to the constitutional court's "fraternity" ruling, activists and others providing humanitarian aid including food and shelter have faced up to five years in prison and fines of 30,000 euros ($35,000), though most people convicted have been given much lighter sentences.