The 35-year-old actress already has a four-year-old son Kahekili with boyfriend Norman Kali, reported Us magazine.
The premiere, which was held at the Dolby Theatre, marked the first time the "Lost" actress walked the red carpet since the "Hobbit: The Battle of the Five Armies" premiere in December 2014.
It is yet to be known when Evangeline is due to give birth.
The brunette beauty previously admitted she loved being pregnant with Kahekili.
"What I wanted originally was six kids. I love being pregnant. I'm one of the lucky women who just had a blissful pregnancy.