The 23-year-old towering forward was out of contract and free to leave the Spireites but incoming manager Dean Saunders, himself a former striker, had expressed a desire to keep him in his squad.
Gnanduillet had loan spells with Tranmere and Oxford last term and has only made 30 league starts in two-and-a-half seasons with Chesterfield, yet new boss Saunders sees him as a key contributor moving forward.
“I’m really pleased,” Saunders told the club’s official website.
“He’s a big, strong young lad and he’s got the tools to be a really good player. I think I can help him, providing he’s got the desire and he wants to listen and take on the information. He has got all the attributes and he can go on and play at the highest level.
“He is the type of player we need as an option, to keep the ball in the box. When we put the ball in, he is a presence. I know he can score – we just have to make sure he gets in the right places.”