Ms Portman, 29, has been acting since she was a child, going from an early role in the Woody Allen film Everyone Says I Love You, to the Star Wars franchise and more recently to the part of a Chasidic wife in the film New York, I Love You.
A Harvard graduate who was taught by Alan Dershowitz while at university, the actress also trained as a ballet dancer on the film.
Ms Portman said: “The character was very interesting to play, always challenging and surprising.”
The Brooklyn-based filmmaker, who is engaged to Jewish star Rachel Weisz, said the cast was excited to launch the film at the festival.
He said: "It is an honour to walk the great red carpet on the Lido.”