The France Under-23 international told Chelsea's website: "I am really excited to be here. It’s just like living a dream to join such a big club. Now I just can’t wait to meet the team and start training."
Blues general manager Paul Green added: "Maelys has good experience for her age and has developed well at Montpellier in the last few years. She is a tall and athletic defender whose profile we believe will suit the WSL. We look forward to seeing her further develop and improve in the upcoming years."