The canton of Gagny is a French administrative division, located in the arrondissement of Le Raincy, in the Seine-Saint-Denis département (Île-de-France région). Its borders were modified at the French canton reorganisation which came into effect in March 2015. Its seat is in Gagny.

It consists of the following communes:

• Gagny
• Neuilly-sur-Marne

• Canton of Livry-Gargan (north)
• Canton of Tremblay-en-France (northeast)
• Canton of Villemomble (west)
• Canton of Noisy-le-Grand (south)

• Cantons of the Seine-Saint-Denis department
• Communes of the Seine-Saint-Denis department

48°53′00″N 2°32′00″E / 48.8833°N 2.5333°E / 48.8833; 2.5333