The Oscar winner plays paraplegic orca trainer Stephanie in the new romantic drama, and she got into character by practising using a wheelchair before the shoot began.
Cotillard admits she found the script inspiring, and used all of her imagination to portray a woman who had lost her legs.
She tells Britain's Film3Sixty magazine, "I try to do the best I can to imagine what it would be and if I'm lucky enough it works. But losing something and being in pain... I know what that is, and then it's just my imagination that works to try to find that authenticity of what it feels like to lose your legs.
"I think it's beautiful to show how someone can survive and be more complete without a part of herself than she was when she had her whole body. Emotionally, it's a beautiful journey to play."