Gérald Bloncourt, who after being expelled from Haiti for his role in antigovernment protests in 1946 went to Paris and turned his zeal for social justice into photography that captured the humanity of immigrants and factory workers, died on Oct. 29 in Paris. He was 91.

His wife, Isabelle Bloncourt-Repiton, said the cause was complications of melanoma.

Mr. Bloncourt’s passion for chronicling the everyday dignity of exploited peoples found a particular focus in Portuguese émigrés who had fled authoritarian rule and conscription to seek jobs in construction and factories in postwar France. For several years, he followed them, on foot and by train, from their villages to makeshift slums outside Paris, where their odysseys ended in renewed hardship in a foreign land.

“I wanted to use my photos as a weapon in hopes to change the world,” he said in Paris in 2013 at an exhibition of his photographs at the Palais de la Porte Dorée.

An immigrant following other immigrants, Mr. Bloncourt showed people in the Pyrenees on their journeys to France and people in the ankle-deep mud of shantytowns in suburbs of Paris like Champigny-sur-Marne. Children stare at his camera from behind chicken wire in front of their shacks. A toddler sleeps in a train car leaving Lisbon. One man gives another a haircut on a rocky road in Champigny.