Tahar Rahim performed his own singing for the movie. Before shooting, he took singing lessons, piano lessons and posturing lessons for months to mimic Charles Aznavour's voice and body language.
As the project was sponsored by Charles Aznavour when he was alive, Tahar Rahim had access to his family, and so to better understand the character Aznavour was, he interviewed his wife, his sister, and his children.
To better fit the part, Tahar Rahim had to lose weight, and also endure hours of makeup with prosthetics every day of shooting.
Directors Grand Corps Malade and Mehdi Idir were personally selected by Charles Aznavour to helm his biopic before he passed away. As it turned out, this happened the day the meeting to start production was scheduled, so everything was shelved for a while, so the directors chose to do La Vie scolaire (2019) in the meantime.
Marie-Julie Baup chose not to rewatch La Môme (2007) before playing the part of Édith Piaf, but she did undergo months of singing lessons and research (watching interviews, concerts, etc.), and like Tahar Rahim, had to undergo hours of makeup every day, with the wig on top of the rest.