The actress stepped out at London's Leicester Square wearing a dramatic strapless Elie Saab shimmering gown that had a fitted bodice and lace embellished sweeping train.
She paired the dress with simple two-strap Christian Louboutin heels in matching navy, and wore her hair loose and straight.
The 25-year-old star looked loved-up as she posed alongside fiancé, actor Boyd Holbrook.
Olsen, who plays nurse Elle Brody - the wife of US Navy Lieutenant Ford Brody - in the upcoming Godzilla remake, also posed alongside her co-stars Bryan Cranston and Aaron Johnson on the red carpet.
Aaron Johnson attended the premiere with his wife Sam Taylor Wood, who also stunned in a fitted black leather dress.