In 1885, he was invited by Juliette Rondeaux, widow of University of Paris law professor Paul Gide (1832–1880) and mother of writer André Gide, to the château de La Roque-Baignard to work as the private tutor of André and direct both his reading and his religious education.
En 1891, Élie Allégret married Suzanne Ehrhardt (1869–1950). They had six children: Jean-Paul (1894–1930), Éric (1896–1971), André, Marc (1900–1973), Yves (1905–1987) and Valentine (1909–1988). Jean-Paul and André were born in Talagouga, in Africa. Éric was born in Paris when Élie was working at the headquarters of the Paris Evangelical Missionary Society in Paris. Filmmaker Marc Allégret was born in Basel, Switzerland, followed by Yves Allégret, also a filmmaker, in Paris where the family had settled in 1903.
Allégret was the tutor and friend of the writer André Gide. The two met in 1885, and quickly developed a deep friendship.
In 1889, Allégret wrote whilst aboard the ship Portugal, en route to Gabon. A significant correspondence maintained their bond of friendship, especially during Allégret's long stays in Africa.
In 1914, after Élie Allégret departed for a mission of evangelization in Cameroon, Suzanne Allégret established her own correspondence with André Gide. Suzanne, matriarch of the family with six children, would recount in detail the activities of each, at the request of Gide.
Pierre Billard, André Gide et Marc Allégret, le roman secret, Plon, 2006
Émilie Gangnat, Élie Allégret, in Patrick Cabanel and André Encrevé (dir.), Dictionnaire biographique des protestants français de 1787 à nos jours, tome 1 : A-C, Les Éditions de Paris Max Chaleil, Paris, 2015, p. 39-40 ISBN978-2846211901
Pierre Masson, Jean Claude, André Gide et l'écriture de soi, Presses Universitaires de Lyon, 2002
Alexandra Loumpet-Galitzine, Njoya et le royaume bamoun, les archives de la Société des missions évangéliques de Paris, éditions Karthala, 2006.
L'Enfance de l'art. Correspondances avec Élie Allégret (1886–1896). Letters of André Gide, Juliette Gide, Madeleine Rondeaux and Élie Allégret, edited by Daniel Durosay. Gallimard, Paris : 1998