Marcel Allain (French pronunciation: [maʁsɛl alɛ̃]; 15 September 1885 – 25 August 1969) was a French writer mostly remembered today for his co-creation with Pierre Souvestre of the fictional arch-villain and master criminal Fantômas.

The son of a bourgeois family, Allain studied law before becoming a journalist.

Investigating Magistrate Germain Fuselier, later to become a recurring character in the Fantômas series, appears in the novel.

Then, in February 1911, Allain and Souvestre embarked upon the Fantômas book series at the request of publisher Arthème Fayard, who wanted to create a new monthly pulp magazine.

On 27 September 1926, Allain married Souvestre’s girl-friend, Henriette Kistler.