The Oscar winner, best known for her roles in Midnight in Paris, Inception, The Dark Knight Rises, and Edith Piaf biopic La Vie en Rose, took to Instagram to announce the happy news, as well as address the rumours that had begun circulating about her involvement in the recent divorce proceedings of Brad Pitt and Angelina Jolie.
Marion stars alongside Brad in the new spy thriller Allied and the pair are said to have great on-screen chemistry.
However, the 40 year old was quick to dispel any gossip about the possibility of any off-screen relationship with the actor, confirming that long-term partner Guillaume Canet is the father of her child, and expressing wishes for Brad and Angelina to 'find peace in this very tumultuous moment'.
https://www.instagram.com/p/BKowf3pghWl/?taken-by=marioncotillard&hl=en'This is going to be my first and only reaction to the whirlwind news that broke 24 hours ago and that I was swept up into,' Marion, who is already mum to 5-year-old son Marcel, wrote to her 401,000 followers.
'I am not used to commenting on things like this nor taking them seriously but as this situation is spiraling and affecting people I love, I have to speak up.'
'Firstly, many years ago, I met the man of my life, father of our son and of the baby we are expecting. He is my love, my best friend, the only one that I need.'
'Secondly to those who have indicated that I am devastated, I am very well thank you. This crafted conversation isn't distressing.'
'And to all the media and the haters who are quick to pass judgment, I sincerely wish you a swift recovery.'
'Finally, I do very much wish that Angelina and Brad, both whom I deeply respect, will find peace in this very tumultuous moment. With all my love, Marion'.