Polanski was educated at the International School of Paris. She later studied acting at the Drama Centre London and the Central School of Speech and Drama, graduating in 2014.

In 2015, Polanski appeared in the British independent film Unhallowed Ground and began portraying Princess Gisla in the History Channel series Vikings. Princess Gisla was introduced in season three of Vikings as a daughter of the French Emperor Charles the Bald (while a legendary French princess named Gisela was the daughter of his grandson, Charles the Simple).

In 2019 Polanski starred in Rene van Pannevis debut feature Looted. Pannevis stated, “I hadn’t worked with Morgane before so she was a bit lost after her first scene. Thankfully, she picked it up very quickly and her performance is beautiful. I mean, growing up in that environment, I knew she had the skills.”

In February 2020 it was announced that Polanski will appear in the Wes Anderson’s new film The French Dispatch.