Hollande, who announced the development during a trip to Slovakia, thanked Niger President Mahamadou Issoufou for the release of Thierry Dol, Daniel Larribe, Pierre Legrand and Marc Feret, France 24 reported. The men are employees of French nuclear giant Areva and its subcontractor Satom.
French Foreign Minister Laurent Fabius and Defense Minister Jean-Yves Le Drian traveled to Niamey to bring the freed hostages home. Fabius told French TV the men were "in good shape."
France 24 said the four were expected to return to France Wednesday morning.
In an interview with TF1, Le Drian denied any ransom was paid to secure the men's freedom. "We don't play that game," he said, adding no violence was involved in freeing them.
The Frenchmen were kidnapped in September 2010 by the North African wing of al-Qaida.
Seven French nationals remain captives in other countries, France 24 said, with two held in the Sahel region, where Mali and Niger are located, one in Nigeria and four in Syria.