Le Gendre was born in Oullins, France the son of Jean-François Legendre-Héral, a noteworthy painter, sculptor, and professor at the L'Ecole de Beaux-Arts [REF].
With the outbreak of the American Civil War in the United States in 1861, Le Gendre helped recruit the 51st New York Volunteer Infantry, and was commissioned a major of that regiment on October 29, 1861.